Here’s a collection of tips you might find helpful the next time a pricey piece of gear stands between you and great recordings.

Help from others

Have a friend perform: Home recording, especially for singer/songwriters and electronic musicians, often involves a single musician writing and recording all the music. But artists in this situation can find themselves too close to the song, at mix time, to make decisions critically.

Working with other musicians might initially complicate recording and mixing. However, creating a great mix depends, in part, on your ability to remove unnecessary details, and most of us are more comfortable objectively critiquing someone else’s work. So asking a friend (or some professionals) to perform a track or two will ultimately make mixing easier, and more effective.

Get more ears on the mix: With any task requiring attention to detail, it’s easy to lose the forest for the trees. And so it goes with mixing. A second or third opinion can draw your attention back to details you’ve glossed over.

And outside opinions needn’t come from other musicians and engineers. (Although the homerecording.com MP3 mixing clinic is a great source for free advice.) Often, regular listeners give the best feedback because they don’t think in technical terms about the production, and instead form their thoughts on how the song makes them feel. And some of the best mix feedback I’ve gotten has come from children, who are unconditioned by musical convention.

Listen on multiple systems: Hearing a mix through different speakers is a little like getting a second opinion. And professional mixing engineers rely on this technique. Chris Lord Alge, for example, keeps a portable radio near his console for checking mixes:

[E]very client who comes in here wants to hear their mixes on it. If it doesn’t sound good through 2-inch speakers on your little boom box, what’s the point? It’s got to sound big on a small speaker.

Simplify …

Avoid dogma: Our hobby (or profession, if you’re lucky) is plagued with religious arguments, like “tube gear sounds better,” and “analog sounds warmer than digital.” Regardless of each argument’s merit, these dogmatic issues over-complicate the recording process, and distract us from the importance of technique – which, of course, costs nothing!

Cut. Ruthlessly: As musicians, our egos push us to put everything we’ve got into every part we record. But virtuoso performances and great recordings don’t necessarily go together. The whole, as they say, is often greater than the sum of the parts.

In most song arrangements, over-instrumentation usually just leads to clutter. And along with being more difficult to mix, clutter rarely sounds good.

Make every part do work: Ensure that every part competing for the listener’s attention is supposed to compete for the listener’s attention.

Practice

Practice your performance before hitting record: The benefits of practice should be obvious to all musicians, but home recording fosters a “write as you record” approach to song creation.

Practice takes time. But it needn’t hamper the creative process; and in most cases it will ultimately save time. Though the tracks may take longer to record, it’s far easier – and quicker – to mix a set of well-performed, polished performances.

Not only do the performances themselves benefit from practice, but the final mix will sound more professional.

Use reference CDs: No single technique will do more to improve the quality of your mixes. Working with a reference mix is, in some ways, like getting a free lesson on mixing from a professional engineer.

Practice mixing when you’re not in the studio: Every mixing engineer should spend time listening critically to professional mixes. Set aside some time every day, say 10 minutes, to immerse yourself in a mix someone else has done. Consider the panning, which instruments take your focus, and how the focus changes as the song evolves. Try to determine the effects in use, and why they were chosen. In modern pop and rock mixes, the interplay between the lead vocal and the snare drum is particularly important, as is the bass guitar/kick drum relationship, so spend some time analyzing these parts in detail.

See Also: Create more professional home recordings

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I address the 10 most common myths, and the truth behind each, below.

Peak Normalization

First, some background: While “normalize” can mean several things (see below), the myths below primarily involve peak normalization.

Peak normalization is an automated process that changes the level of each sample in a digital audio signal by the same amount, such that the loudest sample reaches a specified level. Traditionally, the process is used to ensure that the signal peaks at 0dBfs, the loudest level allowed in a digital system.

Normalizing is indistinguishable from moving a volume knob or fader. The entire signal changes by the same fixed amount, up or down, as required. But the process is automated: The digital audio system scans the entire signal to find the loudest peak, then adjusts each sample accordingly.

Some of the myths below reflect nothing more than a misunderstanding of this process. As usual with common misconceptions, though, some of the myths also stem from a more fundamental misunderstanding – in this case, about sound, mixing, and digital audio.

Myths and misinformation

Myth #1: Normalizing makes each track the same volume
Normalizing a set of tracks to a common level ensures only that the loudest peak in each track is the same. However, our perception of loudness depends on many factors, including sound intensity, duration, and frequency. While the peak signal level is important, it has no consistent relationship to the overall loudness of a track – think of the cannon blasts in the 1812 Overture.

Myth #2: Normalizing makes a track as loud as it can be
Consider these two mp3 files, each normalized to -3dB:

The second is, by any subjective standard, “louder” than the first. And while the normalized level of the first file obviously depends on a single peak, the snare drum hit at 0:04, this serves to better illustrate the point: Our perception of loudness is largely unrelated to the peaks in a track, and much more dependent on the average level throughout the track.

Myth #3: Normalizing makes mixing easier
I suspect this myth stems from a desire to remove some mystery from the mixing process. Especially for beginners, the challenge of learning to mix can seem insurmountable, and the promise of a “trick” to simplify the process is compelling.

In this case, unfortunately, there are no short cuts. A track’s level pre-fader has no bearing on how that track will sit in a mix. With the audio files above, for example, the guitar must come down in level at least 12dB to mix properly with the drums.

Simply put, there is no “correct” track volume – let alone a correct track peak level.

Myth #4: Normalizing increases (or decreases) the dynamic range
A normalized track can sound as though it has more punch. However, this is an illusion dependent on our tendency to mistake “louder” for “better.”

By definition, the dynamic range of a recording is the difference between the loudest and softest parts. Peak normalization affects these equally, and as such leaves the difference between them unchanged. You can affect a recording’s dynamics with fader moves & volume automation, or with processors like compressors and limiters. But a simple volume change that moves everything up or down in level by the same amount doesn’t alter the dynamic range.

Myth #5: Normalized tracks “use all the bits”
With the relationship between bit depth and dynamic range, each bit in a digital audio sample represents 6dB of dynamic range. An 8-bit sample can capture a maximum range of 48dB between silence and the loudest sound, where a 16-bit sample can capture a 96dB range.

In a 16-bit system, a signal peaking at -36dBfs has a maximum dynamic range of 60dB. So in effect, this signal doesn’t use the top 6 bits of each sample*. The thinking goes, then, that by normalizing the signal peak to 0dBfs, we “reclaim” those bits and make use of the full 96dB dynamic range.

But as shown above, normalization doesn’t affect the dynamic range of a recording. Normalizing may increase the range of sample values used, but the actual dynamic range of the encoded audio doesn’t change. To the extent it even makes sense to think of a signal in these terms*, normalization only changes which bits are used to represent the signal.

*NOTE: This myth also rests on a fundamental misunderstanding of digital audio, and perhaps binary numbering. Every sample in a digital (PCM) audio stream uses all the bits, all the time. Some bits may be set to 0, or “turned off,” but they still carry information.

Myth #6: Normalizing can’t hurt the audio, so why not just do it?
Best mixing practices dictate that you never apply processing “just because.” But even setting that aside, there are at least 3 reasons NOT to normalize:

1. Normalizing raises the signal level, but also raises the noise level. Louder tracks inevitably mean louder noise. You can turn the level of a normalized track down to lower the noise, of course, but then why normalize in the first place?
2. Louder tracks leave less headroom before clipping occurs. Tracks that peak near 0dBfs are more likely to clip when processed with EQ and effects.
3. Normalizing to near 0dbfs can introduce inter sample peaks.

Myth #7: One should always normalize
As mixing and recording engineers, “always” and “never” are the closest we have to dirty words. Every mixing decision depends on the mix itself, and since every mix is different, no single technique will be correct 100% of the time.

And so it goes with normalization. Normalizing has valid applications, but you should decide on a track-by-track basis whether or not the process is required.

Myth #8: Normalizing is a complete waste of time.
There are at least 2 instances when your DAW’s ‘normalize’ feature is a great tool:

1. When a track’s level is so low that you can’t use gain and volume faders to make the track loud enough for your mix. This points to an issue with the recording, and ideally you’d re-record the track at a more appropriate level. But at times when that’s not possible, normalizing can salvage an otherwise unusable take.
2. When you explicitly need to set a track’s peak level without regard to its perceived loudness. For example, when working with test tones, white noise, and other non-musical content. You can set the peak level manually – play through the track once, note the peak, and raise the track’s level accordingly – but the normalize feature does the work for you.

Myth #9: Normalizing ensures a track won’t clip
A single track normalized to 0dBfs won’t clip. However, that track may be processed or filtered (e.g. an EQ boost,) causing it to clip. And if the track is part of a mix that includes other tracks, all normalized to 0dB, it’s virtually guaranteed that the sum of all the tracks will exceed the loudest peak in any single track. In other words, normalizing only protects you against clipping in the simplest possible case.

Myth #10: Normalizing requires an extra dithering step
(Note: Please read Adam’s comment below for a great description of how I oversimplified this myth.) This last myth is a little esoteric, but it pops up sporadically in online recording discussions. Usually, in the form of a claim, “it’s OK to normalize in 24 bits but not in 16 bits, because …” followed by an explanation that betrays a misunderstanding of digital audio.

Simply put: A digital system dithers when changing bit depth. (i.e. Converting from 24-bits to 16-bits.) Normalizing operates independent of bit depth, changing only the level of each sample. Since no bit-rate conversion takes place, no dithering is required.

Other Definitions

Normalizing can mean a few other things. In the context of mastering an album, engineers often normalize the album’s tracks to the same level. This refers to the perceived level, though, as judged by the mastering engineer, and bears no relationship to the peak level of each track.

Some systems (e.g. Sound Forge) also offer “RMS Normalization,” designed to adjust a track based on its average, rather than peak, level. This approach closer matches how we interpret loudness. However, as with peak normalization, it ultimately still requires human judgment to confirm that the change works as intended.

Most importantly: Every voice is different, and every song is different. That advice bears remembering, even if you’ve heard it dozens of times. When you find yourself approaching a vocal mix on auto-pilot, applying effects “because they worked last time,” consider disabling the EQ altogether to gauge just how badly the adjustments are needed.

Reasons to EQ: The 3 main reasons to filter a vocal with EQ are
 1) to help the voice sit better in the mix,
 2) to correct a specific problem, and
 3) to create a deliberate effect, like “A.M. radio voice.”

If you’ve EQ’d a vocal track for some other reason, be sure the result is improving the mix.

Gentle boosts: The “cut narrow, boost wide” guideline applies to vocals perhaps more than any instrument. Our ears have evolved remarkable sensitivity to the sound of human speech. (Consider how easily we pick up a single conversation in a crowded noisy room.) So we’re immediately, instinctively aware when a voice has been processed unnaturally.

High-pass: Most vocals – though of course not all – benefit from a low cut filter. The average fundamental frequency in an adult male voice is 125Hz, and often you can roll off up to 180Hz without affecting the sound. (If your mic or preamp has a low-cut filter, consider engaging it when recording vocals, as most subsonic audio in a vocal track consists of mic-stand noise, breath rumble, popping, and other undesirable sounds.)

Bypass: Especially with high-pass filters, it’s easy to remove too much body from a vocal, as our ears adjust so quickly to new sounds when mixing. If your EQ has a bypass option, use it periodically to make sure you haven’t gone too far with an adjustment.

Common fixes:

• To reduce a nasal sound, try dipping a few dB around 1kHz, and moving the center frequency slightly up or down to find the most effective point.
• To treat popping P’s and T’s, cut everything below 80 Hz.
• For a little extra clarity and presence, try gently boosting the “vocal presence range” between 4kHz and 6kHz.

Reasons NOT to EQ: EQ can’t make your voice sound like someone else’s.

See Also: Better vocals improve your recordings, Great free vocal plugins

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So, listen here to 10 of pop music’s most blatant auto-tune abuses:

If you’re unfamiliar with Auto-tune, and especially if you listen to much pop and rock, you might not hear it initially. When overdone, the effect yields an unnatural yodel or warble in a singer’s voice. But the sound is so commonplace in modern mainstream music that your ears may have tuned out the auto-tune!

The songs in this clip, in order, and the phrases most affected by auto-tuning to help you spot them:

Dixie Chicks – The Long Way Around – Noticeable on “parents” and “but I.”

T-Pain – I’m Sprung – Especially obvious on “homies” and “lady.”

Avril Lavigne – Complicated – Listen to “way,” “when,” “driving,” “you’re.”

Uncle Kracker – Follow Me
The whole vocal sounds strained, but especially the word “goodbye.”

Maroon 5 – She Will Be Loved – Listen for “rain” and “smile.”

Natasha Bedingfield – Love Like This – “Apart” and “life.”

Sean Kingston – Beautiful girls – “OoooOver” doesn’t sound human.

JoJo – Too Little Too Late – Appropriately, “problem” stands out.

Rascal Flatts – Life is a Highway
Every vocal, foreground and background, is treated, but “drive” in particular.

New Found Glory – Hit or Miss – “Thriller”, and every time Jordan sings “I.”

The Cher Effect

When used noticeably, an auto-tuner produces what most call “The Cher Effect“, named for her trademark sound in the song Believe*. (In essence, we named the effect like scientists naming a new disease after its first victim.) Treated this heavily, a vocal track sounds synthetic, and obviously processed.

But not all auto-tuning is so blatant. In the sample above, it’s harder to hear the pitch correction on Uncle Kracker and Avril than on T-Pain and Bedingfield.

Tasteful Uses

As with any tool, a little care can yield great results. Some simple things to keep in mind about pitch correction tools:

• Performance: Most importantly, an auto-tuner isn’t a shortcut to a perfect performance. If you can’t sing the song properly, no amount of post-processing will make it sound like you did. So when your pitch matters, and you don’t want to correct it with an effect, you’ll need to work on your performance until it’s right.
• Less is more: The fewer notes you correct, the less obvious your use of an auto tuner will be. Consider automating the plugin so it acts only when most needed.
• Graphical mode: If your pitch correction software offers a graphical mode (like Antares Auto-Tune and Melodyne,) learn how to work with it. The default “auto” modes are OK for basic corrections, but often produce noticeable yodeling.
• Backing vocals: In general, you can get away with more pitch correction on backing vocals than lead vocals.
• Outdated: Obvious vocoder-style autotuning is dated, and borders on kitschy. The synthetic warbling vocal sound marks songs as having come from a specific era, the same way gated-reverb on drums instantly places a song in the 1980’s. Remember: If you make the auto tuner obvious, people will say your song uses “the Cher effect.” Let this be a guideline.

Be sure it’s needed

Two songs have auto tuners on my mind today: Snoop’s Sensual Seduction (because of Anil Dash’s ruminations on the death of the analog vocoder,) and Natasha Bedingfield’s Love Like This, which I heard on the radio. In the former, the auto tuner is clearly a gimmick. But every time I hear Bedingfield’s song, I’m struck by the same question: Why do that to her voice?

She’s a fantastic singer, and once you’ve heard the song without the cheesy auto tuner effect, it’s hard to take the radio single seriously.

And there’s a lesson in that for home recordists, (even those of us who don’t write pop music,) which echoes the rule of mixing: If an effect significantly changes the sound of a track, especially one so important as the lead vocal, be sure that change improves the song before committing it to the mix.

See Also: The Rule of Mixing

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In effect, posing one of these questions tells the world you’re an amateur. But I hope that by explaining why the questions don’t have the simple answers a rookie expects, you’ll appreciate how an experienced engineer thinks about each problem, and be better equipped to identify gaps in your own knowledge.

Questions

1. What are the best EQ settings for guitar?
Or its many variants: “What are the best compressor settings for vocals,” “what reverb settings should I use for mastering,” and so on.

This question has a straightforward answer: The best settings are the ones that sound right. But for most beginners, who haven’t yet learned critical listening skills, this advice seems trite.

Unfortunately, any other answer is meaningless. Every track, in every song, has its own unique requirements. And the best settings, for EQ or compression or any effect, are dictated solely by the requirements of the song. (See the Rule of Mixing for more.)

2. Which is the best microphone?
We’d all love to own a U87 or a C12. But engineers covet those mics because they’re reliable and versatile, not because either is inherently superior. In fact, there are as many ways to define “best” (and for that matter “worst”) as there are sounds to record. As with the question above, what’s best ultimately depends on what fits the song.

3. How do I record my song to sound like The Foo Fighters?
This question stems from the misconception that The Foo Fighters, or any band, sound the way they do because of their equipment. Acquire the same instruments and mics, the thinking goes, and you can duplicate their recordings.

Most professional recordings have deceptive clarity. They sound, at least to listeners unfamiliar with the process, as though they should be easy to reproduce. But the question above has only one honest answer. To sound like The Foo Fighters:

• Buy quality instruments, and learn how to play them well.
• Write songs suitable for the genre.
• Arrange those songs to support Foo Fighters-style production.
• Practice. Lots.
• Record in a great live room.
• Spend time on microphone selection and placement.
• Play every part till you get it right.

In other words, there are no shortcuts, and it’s not easy. Great recordings take time and talent.

4. What vocal chain does Paul Simon use?
Also commonly worded as “I want to sound like John Mayer. Which microphones and settings should I use?”

Beginners ask this question assuming that we can recreate a track by knowing how it was recorded. Unfortunately, even if you bought Paul Simon’s complete signal chain, you’d have little success matching his recordings. His voice, and John Mayer’s voice, and of course the voice of any famous musician, is unique, as are his performances.

To sound like Paul Simon, in short, you need to have him sing your vocal

5. How do I remove the room’s ambiance from a recording?
Conceptually, it makes sense that since we use reverb to add depth, there must be some way to reverse the process.

There isn’t. If you don’t notice until you’re mixing that a guitar track has too much room sound, you have 2 options: Live with the sound, or re-record.

6. Is this mix finished?
Rookie engineers like to think there’s a golden standard sound to which they aspire, and once they’ve attained that sound, their mixes will thereafter be perfect.

We should be so lucky! In truth, our learning never stops. We continue (hopefully) to improve, but none of us is ever done acquiring knowledge, as true of recording and mixing as it is of life. But this is OK. Learning, after all, is the fun part!

To the question: As a general guideline, a mix is finished when it best represents the song. Of course, “best” is open to interpretation here as it is everywhere in recording. You need to use your ears and your gut, and make the call when it feels right. In other words, only you know when the mix is finished.

Unless someone has paid you, in which case the mix is done when the deadline arrives.

Finally, a surefire question to signal your newbie status to the world:
7. How do I use this $1,200 plugin that I just happen to have installed on my machine?
Answer: You read the manual, which comes with the software when you buy it legally.

In Closing

You’ll out yourself as a novice by asking these questions of an experienced engineer. But really, there’s nothing wrong with that. In some senses, we’re all amateurs.

Take the colleague of my friend Paul, who once asked him, “what does a compressor do?” The question seems innocent enough until you learn that this colleague has been a film industry sound engineer for over 20 years, and has worked on dozens of major motion pictures. Of course, Paul now has difficulty taking his colleague seriously as an audio professional. But the guy still works on movies as a sound engineer, so the anecdote should be comforting for the rest of us amateurs!

See Also: Tips for more professional recordings

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In particular, I own and love Naomi Epel’s Observation Deck. If I sense a creative lull creeping on, I pull out a card and ponder its message (for example, “think in reverse,”) and invariably, almost like magic, my brain’s off and running again.

The Observation Deck isn’t free. But these 3 web sites, offering similar imagination exercises, are.

Mixer’s Block

It turns out that, along with helping writers, these tools are great for halting mixer’s block. Mixer’s block is exactly what it sounds like: The mixing engineer’s version of writer’s block.

You’ve likely found your mixes fall into two categories: Those that take care of themselves, and those that take years off your life. No amount of knob tweaking and fader pushing seems to bring resolution to those in the second category. Blocked mixes instead wait interminably on a flash of creative insight, for despite its technical nature, mixing is often art more than science.

Like its counterpart for authors, mixer’s block is frustrating and energy-zapping. And this is where the tools above come in. They’re designed to help shift your thinking, to inspire ideas from parts of your brain you’ve forgotten to use. Like a “virtual outside opinion,” it’s often all a stalled mix needs.

In practice

Let me illustrate with an example: I pulled hair out mixing Pushed Around. The mix wouldn’t jell. After fighting with it for hours, I decided to consult the Observation Deck, which told me to “create a conflict.”

Instantly, I realized the acoustic guitars were in conflict, fighting each other for the listener’s attention. I nudged the guitar tracks into better alignment, added the shaker to emphasize the beat and distract from the guitar strums, and the mix immediately righted itself.

This can work for any mix. So the next time you find a troubling mix uncooperative, consider setting the technical details aside and letting your imagination suggest new approaches. “Try faking it,” perhaps (a personal favorite,) or maybe even “think about the last time you cried.”

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Of course, no two listeners hear music the same way – a truism easily proven by arguing with Linkin Park fans about what constitutes good rock – and mixing engineers themselves must contend with this subjectivity in our senses. But it often appears that music production lacks any rules; that mixing engineers essentially just follow their whims behind the console.

No “rules,” just “rule”

Indeed, most so-called “rules of mixing” are no more than guidelines. For example, “boost EQ in wide bands,” and “use a slower attack when compressing drums.” Both are great tips, but hardly true in all situations.

However, one overarching principle does apply in every mix, to every song, and to every mixing engineer. I think of it as the Rule of Mixing:

Though it may at first appear trite, this rule simply and powerfully covers the fundamental practices of mixing. A good mix supports the song, presents only what the listener needs to hear, and leaves out unnecessary distractions. Good mixing, in turn, requires keeping the rule in mind at all times to accomplish these goals.

Implications

Some of the rule’s most important implications:

Have a plan
How can you reliably judge which effects and fader moves to keep? In short, by knowing before you start mixing what you want to achieve. Mix with a clear plan in mind for the song, and every change that doesn’t get you closer to this goal is simply not needed.

Don’t use effects “just because”
If you routinely, automatically high-pass guitar tracks, or compress the kick drum and bass guitar, you’re probably violating the Rule of Mixing. Decide before adding one of these effects whether it’s really needed this time. Worded another way: Just because something worked on your last 5 mixes doesn’t mean it’s right for this song.

“Improved” can mean many things
Note that the rule doesn’t say “only do that which improves the sound” (with emphasis on sound.) Sometimes, in order to improve the end result, you need to destroy the sound, for example by adding distortion, or creating a lo-fi mix. This is perfectly OK, if that’s what the song requires.

Mixing starts long before you move the first fader
Taken to its logical extreme, the Rule of Mixing implies that in a perfect world, a mix would require no changes. Just bring the faders up, and you’re done. While that’s obviously impractical, it’s still a great thought to keep in mind when recording. The closer a recorded sound comes to the required final result, the easier it will be to adhere to the Rule of Mixing. This suggests, and not by accident, that you should form your mixing plan even before you start recording!

Favour simplicity
An important corollary to the Rule of Mixing holds that the simpler of two identical-sounding signal chains is always preferable. If you add a plugin but don’t hear a difference, the plugin doesn’t belong in your mix. Whether the effect was too subtle to detect, or your ears simply can’t hear any change, the end result is the same: If you can’t confirm that the change is an improvement, then it’s not needed.

It’s easy to bloat a track with plugins designed to add character or warmth or depth – stereo enhancers, tube and tape simulators, harmonic distorters. But while these tools serve a purpose, their use should always be secondary to your main goal: Improving the song.

Be honest with yourself

More than anything, the Rule of Mixing keeps mixing engineers honest with ourselves. Music is subjective, for listeners and creators alike. But with the constant awareness that every change we make must improve the end result, we force ourselves to think of the mix as a bigger picture.

Phil Spector and Glyn Johns got different end results because they approached their respective mixes with different plans. But both mixes sound great, and emphasize The Beatles’ songwriting, a sure sign that both engineers followed the Rule of Mixing.

See Also: lots more mixing tips!

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Under specific conditions, which I describe below, the DAC can produce an analog signal that momentarily exceeds the level of the digital signal from which it was converted. This is known as an inter-sample peak, and while it may at first seem just a curious side effect of the conversion process, these peaks have implications for anyone working with digital audio. And in particular, engineers who like “hot” mixes.

Digital Audio – grossly over-simplified

Computers process numbers, so to work with audio in a computer, we must convert the sound into numbers. This is accomplished by “sampling” the audio signal at regular intervals – 44,100 times a second for CD audio – and saving the observed level. The diagram below illustrates this, albeit crudely. The samples in red, numbered 1 to 9, represent a sequence of signal levels observed by the recording interface.

You can see something similar by zooming-in on a waveform in any recording software. The “step-ladder” model illustrates the discrete samples of digital audio, with levels ranging from “-inf” (silence) to 0 dBFS (the loudest sound a digital system can represent [*]) However, sound outside a computer doesn’t move through the air in jagged, abrupt steps. Rather, it moves smoothly and continuously – more like the blue line in this diagram.

Digital to analog conversion, then, is essentially the creation of the smooth blue analog line from the set of stepped red digital samples.

Intersample peaks

Occasionally, the smoothing yields an interesting result, illustrated below. Note that in order to generate a smooth curve between samples 5 and 6, the DAC produces a signal that peaks higher than either of the samples. This is an inter-sample peak.

This diagram also illustrates the main issue with these peaks: Samples 5 and 6 are both at 0 dBFS – that is, they represent the loudest sound the digital system can reproduce. Yet the peak analog signal reconstructed by the DAC exceeds this level.

In short, the DAC in this example has generated an invalid signal.

How does it sound?

What this means in practice depends on a few factors, including the quality of the DAC, and the signal chain after the converter.

In the worst case, the example above would result in audible clipping when the system tries to generate the illegal voltage. But even if no clipping occurs, the analog side of the DAC will only handle the signal cleanly if the DAC’s analog circuitry has some headroom. If the DAC’s designers assumed that 0dBFS is the loudest signal the converter will emit (technically, a valid assumption,) then an analog peak above this level will cause distortion.

Here’s a short clip I deliberately mixed hot. There’s no digital clipping (the maximum sample level is -0.1dBFS,) but there are lots of inter-sample “errors”, including a nasty string of them at 0:13.

If you hear any pops or clicks, it’s a good sign that your setup doesn’t allow for inter-sample clipping. Most likely, though, the track sounds just fine to you. Many systems, especially those equipped for mixing audio, allow some head room between the maximum digital signal level and the onset of analog distortion.

But not every system… If you mix hot, especially if your meters peak within 1dB of full scale, your mixes probably contain these peaks. And though your DAC protects you, there’s no guarantee that your listeners have quality converters. In other words, you may be sharing clipped or distorted audio without realizing it!

Preventing inter-sample clipping

There are at least 3 ways to ensure your mixes don’t generate inter-sample distortion:

1. Leave lots of headroom in your mix: This is the obvious solution, and it requires no special processing. As long as you keep the peak levels in your mix below 0dBFS, the DAC will never encounter the situation described above. The consensus I’ve found is that real-world inter sample peaks never exceed 1dB, so keep your levels below -1.0 dBFS and you’ll be fine.

2. Use a mastering tool designed to prevent these peaks: iZotope’s Ozone is one such tool. The loudness maximizer has a one-click option to prevent inter-sample clipping.

3. Use a metering tool that highlights the peaks: SSL recently released the X-ISM Plug-In which adds an inter-sample peak meter to any VST-capable DAW.

X-ISM uses significant processing to provide a combination of up-sampling and filtering that mimics the operation of an oversampling DAC’s reconstruction process. The result is a meter that shows inter-sample errors and provides a useful tool that most DAW metering misses.

More reading

Along with the page on SSL’s site, above, here are a few more links that explore the issue in detail:

- 0 dBFS explained

- Chris Tham’s Issues with 0dBFS+ Levels On Digital Audio Playback Systems

- This classic thread on ProSoundWeb (especially the posts by Paul Frindle) presents head-spinning amounts of information. I recommend re-reading it every few months.

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Inspired by “engineering screw-ups” on Gearslutz, here’s a list of recording and mixing bloopers that made it past the mixing room onto the final release.

These aren’t performance missteps, where the band missed a cue, or the singer came in too soon. There are certainly countless examples of those but most were included intentionally, to add character or realism. Rather, the flubs below highlight mistakes in recording or mixing that could have been corrected before the track was released.

Some of the mistakes probably went unnoticed. Some, I’m sure, were noticed and begrudgingly accepted because of a deadline. But reassuringly for us amateurs, they all prove that even the pros aren’t perfect.

Botched Edits

The edit in question happens at 0:09 in the clip below. I scratch my head every time I hear it. So many questions: What went through the mixing engineer’s head? Why didn’t Clapton object? What’s powpower?

Recording and mixing engineers traditionally build a vocal track by “punching in” (re-recording a rough spot) and “comping” (building a single vocal track from the best parts of multiple takes.) Before digital editing, this was a manual procedure prone to timing errors. So the example above, recorded in 1970, is forgivable (although puzzling, because it’s so obvious.) Today, however, it’s common practice to digitally automate the punches and comps, which means the next two examples really shouldn’t have happened:

You was the first track on their first album, so the band surely aimed to make an impact. And without question, Thom Yorke bellowing high A for 8 seconds is a great hook, perhaps even the song’s defining moment… until you realize that his wail is comped from shorter sections. Listen for the cut at 0:05:

Notice how the vocal timbre changes in the middle of the word “yeah”, after “eyes deceive me.” I can’t fathom how this edit made it to mastering. Unlike the Radiohead example, which is only obvious on close listen, this cut simply sounds distracting!

Here, the tonality changes completely at 0:10, and again at 0:30. Lennon supposedly recorded a demo on his home tape recorder, and at mix time, he and Phil Spector (who produced the track) preferred the emotion in the home recording for one verse only.

Strange noises

This is the best example of John Bonham’s notoriously squeaky bass drum pedal. Jimmy Page discussed the squeak in a 1993 Guitar World interview:

The only real problem I can remember encountering was when we were putting the first boxed set together. There was an awfully squeaky bass drum pedal on “Since I’ve Been Loving You”. It sounds louder and louder every time I hear it! [laughs]. That was something that was obviously sadly overlooked at the time.

Some lessons I’ve learned from The Beatles:

• All you need is love.
• The walrus was Paul.
• If you drop a tambourine while recording, stop the tape and re-record.

I can see this slipping by unnoticed because it almost sounds musical. Almost. But listen to the clip a few times, and it becomes obvious just how out of place that tambourine is. (For more details, check out What Goes On, a fantastic reference for the little nuances like these in Beatles recordings.)

As Aguilera sings, you’ll hear a faint rhythm track in the background. This is headphone bleed – sound leaking from her headphone monitor into the microphone. (Note: I boosted the high frequencies on this track to make the bleed more obvious.)

Dave Pensado, who mixed Beautiful, discusses the noise here:

The song was about being beautiful and honest in EVERY way. That bleed is honest. It was one of the most honest vocal performances I had EVER heard. It was actually the scratch vocal.

This is another cop-out. Mixing engineers have their own version of the fourth wall, and Pensado broke it with this mix. Honest or not, the bleed reminds listeners of the technology used to record, and that distracts us from Aguilera’s performance.

Technical screw-ups

As Rick Wright holds the last piano chord, the tape speed wobbles for a second:

This clip plays two phrases from the 2nd verse of Roxanne. Compare the reverb tail at the end of “night” and “right.” The first decays naturally and cleanly, the second ends abruptly.

Does Natalie’s voice sound odd to you on the word “parents?”

Lessons

These clips hold a couple of lessons for amateur producers and home recordists:

1) You don’t need to be perfect. The pros know this. Most mistakes will simply go unnoticed, some mistakes add character, and sometimes a looming deadline trumps all.

2) That said, there’s no excuse for releasing sub-par material when you have the time and the skills to improve it. The Incubus, Dixie Chicks, and John Lennon examples especially are obvious to the point of annoyance, and mostly just make the mixing engineer seem lazy!

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Try lowering the volume: Along with checking a mix through different speakers, it helps to listen for elements that jump out at different volume levels. In particular, spend some time with the mix turned way down. Thanks to equal loudness contours, our ears perceive bass frequencies differently at low volume, so mixing quieter can make it obvious when your bass levels are off. It also forces you to listen a little closer!

Skip the cheap reverb: If you have a choice between a low-quality reverb or no reverb at all, leave the track dry. When it’s not used as an obvious effect, we generally add reverb to restore a sense of natural space to close-miked tracks. However, cheap reverb sounds unnatural, and your listeners’ ears will sense this immediately. (Read more about why you should avoid cheap reverb.)

It’s easier to mix well-recorded tracks: Trite as it sounds, tracks that are recorded properly are easier to mix than tracks with problems. Any mix will only sound as good as the players, instruments, and equipment used to record it. If you’re having difficulty mixing a particular track, consider re-recording it …

Previously: Mixing tips, More Recording and Mixing Tips, The Big Page of Mix Tutorials