But our brains also use other cues to determine distance. For example, human hearing excels at matching a sound with the echoes and reflections it causes, to localize its source. And we can apply this principle to add realism when creating the sound stage in a mix.

The Speed of Sound

Consider this picture, and the accompanying audio samples below.

In the scenario illustrated above, sound from the guitar reaches the listener almost immediately, whereas the reflections off the rear wall make a 40-foot round trip, and therefore arrive 40ms later. (Sound travels approximately 1 foot per millisecond.) With the drum kit, on the other hand, the direct and reflected sounds arrive at almost the same time.

The series of events goes something like this:

Our ears and brain are sensitive to these differences in sound arrival time, and use the information (along with other cues, like volume) to judge where a sound source is located in the space around us. Our brains know that sounds and reflections arriving together at our ears must have originated close to a wall, where sounds that arrive much before their reflections must be close to our ears.

Hear it in practice

Here are two short instrumental samples, both mixed from the same raw tracks, to illustrate how this can apply in a mix.

In the first sample, I’ve placed the drums closer by adding a delay between the direct drum sound and the reverb, so the reflections arrive 40ms later than the direct sound – which tricks our ears into hearing a 20ft distance between the drums and rear wall, as with the guitar in the above diagram:

In the second sample, I’ve simulated moving the drums further back by having the direct sound and reverb occur together, both 40ms later than the guitar.

Note that the levels are the same in each clip. I changed the delay times only, to illustrate the effect.

Issues

Caveat: The illustration above is grossly over-simplified. Sounds in a real room reflect off all the walls and surfaces, not just the rear wall. And our ears depend on much more than just timing differences to determine distance. But for the technique at hand, those complications generally aren’t important. The idea here is to trick listeners’ brains by exploiting a property of their sense of hearing, and whether there’s one wall or 4, human ears and brains interpret reverberant sounds the same. (If your listeners are mostly non-human, then all bets are off.)

Implementation: In Sonar, I configure sends (i.e. busses) with delay plugins for each delay time that I need, and I route tracks accordingly. But any platform that allows bussing or routing the signal can accomplish the same end result. So long as you can independently control the delay on the direct sound and on the reverb, you can manipulate the relationship between the two as described above.

Other levels: In practice, you’ll also reduce the level of the drum kit somewhat to make it sound more distant, and adjust the reverb level as required to make the effect more obvious.

Pre-delay

As an addendum: Most reverb units and plugins have a pre-delay setting for controlling the delay between the input sound and the reflections it generates. Pre-delay serves exactly the same function as placing a delay between the direct sound and the reverb. In essence, it “moves” the sound further from the simulated reflecting surface. So if your reverb unit or plugin supports pre-delay, you can accomplish much of the above technique without a separate delay plugin.

And remember this simple guideline when using reverbs for realistic 3d sound stages: To bring a sound forward in the mix, increase the pre-delay.

See Also: Reverb on kick drum, Reverb possibilities

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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

Spring and plate reverbs are the easiest designs to implement. Though depending on your skill with a soldering iron, you can also build an electronic reverb. And capturing the natural ambiance of a space, with a speaker and mic, offers almost unlimited possibilities.

Here’s a collection of links to the Web’s best plans for these homemade reverbs:

Spring Reverbs:

• The most comprehensive design I’ve seen: The Slinky Spring Reverb.
• Some variations on the Slinky design, including a stereo spring reverb.
• A cabinet-style spring reverb for guitar.
• The $2 spring reverb, built from a toy echo mic.
• And finally, a no-frills dirt cheap design.

Plate Reverbs:

• The definitive plate reverb design comes from TapeOp magazine.
• A no nonsense approach, from a poster on the electro music forums (copied here because the site is frequently unavailable.):

I got a sheet of steel, about the size of a very large refrigerator, this was about 1 X 2 meters more or less. I built a wooden frame of 2X4s. Two holes were drilled near the top of the plate and it was suspended to hang on two wooden dowels through rubber grommets.

I took an old 12″ speaker and cut the metal cage off of it and trimmed the speaker cone so as to only have about 1″ from the driver. Then I built a wooden cross member across the plate but not touching it to hold this speaker and glued the shortened cone to the plate. I attached a contact microphone to the plate. I drove the plate through a 50 watt amplifier connected to the speaker (glued to the plate) and took the signal from the contact mic. The placement of the mic is determined by experimentation. I built a simple wet/dry mixer. In those days people built their own circuits. Today I’d buy the mixer.

This entire apparatus was in the basement below my studio.

Electronic Reverbs:

• A collection of schematics for various reverbs.
• Many effects pedal schematics, including a few reverbs.

Natural reverbs:

• Electronic Musician’s Keeping It Real article describes some great approaches to capturing natural reverberance (including a washer or dryer, and an old Gibson guitar.)
• Upload an audio file to Silophone, and hear how it sounds played through speakers in a grain silo.

But when used sparingly, a tight short reverb effect can add body and punch to a dull kick drum. This is especially useful in home recordings where the drums are often dry samples, or tracks recorded in bedrooms and basements with poor live sound.

Here’s an example to illustrate how reverb can beef up a bass drum. As I mentioned in The Morning Rain post from which I took the sample, I used a no-nonsense mic arrangement: Stereo room mics, a single mic on the kit, and an SM58 in the kick drum.

Here are the drums as recorded, with the kick drum track untreated:

In the next sample, I added a short reverb tail to the kick drum only. I used the Kjaerhus Classic Reverb for this example (though there are a few other free reverb effects listed in the great free vocal plugins post, including Mac-based options.) I set a room size of 65 square meters, dampened as many high frequencies as possible, and blended the signal on the dry side.

Here’s how it sounds:

The effect is subtle, but obvious.

Though it’s more obvious in the solo’d kick drum track. The first 3 hits in this next sample are dry, and the last 3 have the reverb applied. Notice how dead the kick drum sounds by itself (I recorded it with an SM58, after all,) and how much more body there is to the tone with reverb applied:

Some notes about this technique:

• It works best on sparse tracks, when the drum hits have space between them. If the track is already dense, adding reverb usually just yields mud.
• It will work on miked or sampled kick drums, but it’s most effective on dry, flat sounds. Basically, if you’re stuck recording your kick drum with an SM57, a little reverb can work wonders to deliver usuable tones.

Previously: Better drum mixes with a drum reference track, Parallel compression for fatter drum tones

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Typically, the plate is a large sheet of steel suspended in a tubular steel frame. In theory, the plate simulates a large concert hall, or church, with a decay time of approximately five seconds at approximately 500 Hz. A driver attached to the plate excites it, and as the sound waves travel through it, the plate flexes. The plate’s motion is then picked up by one or two contact mics, and added to the dry signal at the mixer.

The project isn’t for the timid. But if you’re handy, and have a large sheet of steel lying around, an authentic plate reverb could add a distinctive touch to your recordings.

Previously: Create your own reverb

The first article Adding Effects to Vocal Tracks looks at compression and gating to clean up the vocal sound, with a good overview of various approaches to reverb.

Gates allow an audio signal to pass through them if the signal is above a specified threshold. When the signal is below the threshold, the gate closes, attenuating the signal partially or fully. Gates are utilized to allow the desired (louder) signal to pass through to the output while denying unwanted (softer) signals. They’re useful for eliminating unwanted noise on tracks (like headphone bleed or even the singer’s breathing), for creating cool effects like cutting off reverb tails, and many other applications.

The next article, Adding Ambient Effects to Vocal Tracks, delves more deeply into the use of reverb, delay, and chorus to add depth and character.

Putting your delay effects in stereo can really make your mixes sound wide and deep. You can pan your source track to one side and a delayed signal to the other side. Or you can put the source in the middle and pan delayed copies of the source to each side. For this to be effective, select different delay times for each side of the stereo field. A good technique for thickening a vocal part is tripling the original track by using single delays panned left and right with delay times of 16 ms and 32 ms

… for all its wonders, digital reverb is not indispensable, nor is it always the best way to impart a convincing sense of space to your recordings. Does anyone really think that, for example, Miles Davis’s Kind of Blue would sound better if PCM70s had existed in 1959? Would Led Zeppelin’s “When the Levee Breaks” still hold up today as a zenith of rock drum tones had the kit been close-miked and swathed in digital reverb?

Hot-water heaters, it seems, make great reverb tanks, and a washer or dryer can make a distinctive-sounding reverb chamber.

Record flat with no effects and instead find the right microphone for the singer. In the mix, roll off everything below 100 Hz and above 12,000 Hz. Add 2-4dB at 160Hz for male vocals or 320Hz for female voice for warmth. Notch out the mid-range, 500-800Hz, by a few dB. Sometimes a little sparkle in the 7-8kHz area is good, if there’s no sibilance there. Finally, a little compression after the EQ can smooth the vocals out nicely.

There are also some tips for doubling vocal tracks, and tweaking reverb for vocal settings.

Another way to save CPU resources is to use two instances of a power-efficient mono reverb plug-in to create a unique stereo effect … That approach offers interesting sonic possibilities and also works with hardware processors.