AUDIO TIPS: Acoustics and Recording


Here are some acoustics and recording concepts to consider when recording and mixing. You may discover others as you go along.
This is a huge topic but other musicians and engineers have asked me about this stuff so here are some things to think about while you are recording and mixing. I've included the various questions in this document. Questions like please explain sound propagation, mic polar patterns and standing waves and how to deal with small recording environments. You can click on the links for further investigation.

I try to think of how the end result will sound before I start recording. So try to get the instruments to sound the way you want them to before you start recording. Select a track or album concept that you want your recording to sound like because when you are finished you are going to put this track in your sequencer right next to your mix to A/B with.

Keep options open like recording a clean guitar and a distorted guitar and use a plug in that can be removed or changed later. When we record instruments or voice we are recording the environment as well. And decide how much of the environment you want in your source track? Some engineers want every thing dead and to use processors after the recording has been completed. Others like to reamp sounds later. Meaning after you have recorded you route the signal back out into the room to alter it in some way. The sound propagation and dispersion at the source of the instrument that is being recorded is usually multi directional and the decision to capture the defused reflective waves is a decision that will affect the character of the recorded sound. Think about the song and where it should live sonically. The musical style will often have the answer in it. Sometimes if too much space is captured depending on the source the attempt to blend with other instruments can be a challenge. The distance of four or five feet from the instrument or voice would be considered a room mic. So having a close mic and a room mic will give you the opportunity to have a choice as well as blend the two together.

The mic proximity or how close to the source the mic angle and polar pattern become an important pre-design because the more room sound blended with the source signal the further away the source will sound. Unless you are using an omni mic with a figure eight polar pattern and this captured room ambience as well. In this case the microphone is in a figure eight pattern and one side might pick up the floor tom and the other side is hearing the distant reflection from a 14 foot ceiling. Another thing to try in mind is to place a close mic on what ever you are recording and try two room mics the 3rd mic at the greater distance, then blend the three mic signals together for the sound.

Room and close space and upfront blend very well with one another. EQ the mics a little different in the stereo or surround spectrum. If there is too much low frequency information a mix can get muddy. So use a high pass filter and roll off some of the low end on everything in the mix except the bass guitar and the Kick. If you are recording everything in one room, let’s say a rhythm section, use partitions to isolate the instruments from one another. Even if you are unable to completely isolate all the instruments you will have a lot more sonic control at mix time. If you don’t have any partitions you can make them out of plywood and foam. Or you can experiment with reflective defused or absorbent surfaces. The links in this document will lead to further explanation. Basically get the drums surrounded. Throw a blanket over the kick with the mic inside. Put some gates in the inserts in your software and just let the attack of the drums be dominant.

Snare top and bottom and gate all the toms as well. Face the base amp and guitar amp at the left and right walls at the sides. Angle them facing at an angle from the wall. The mic's focus will be capturing the speaker and the reflection from the wall. Put a blanket over the amp and prop up something that won't rattle to keep the blanket both in place and up the side of the wall a bit. The mic is inside. You might still get some bleeding on the base and guitar tracks. If some of the drums and cymbals bleed into the base and guitar track you can roll off a little of the hi frequencies on the base or guitar. Put a high pass filter on the guitar; that let’s the highs through but then carve out the extreme highs above 10.000 cycles. This will help remove the cymbals from the guitar track. Roll off the lows on the guitar where the bass and kick live sonically. Experiment to find what is right for your mix. If you need to just put all the miced instruments in separate rooms and have everyone in headphones as you record.

Another way is to do a scratch track of the basic song structure say guitar a vocal or piano and vocal to a click. Be sure to set up bars and beats and select the grid quantize resolution. This way when you over dub your drums and other instruments you can quantize everything to the grid if you want to tighten things up. Acoustic treated and non treated environments might have reflective, defused and absorbent acoustic conditions that can be sculpted into the sound. A natural subtle reflective environment is more desirable than using a processor to me But in the studio it is all about controlling the signal and placing all the instruments in the best frequency for itself in the mix. If you get the source to sound the way you want it to then it’s just a matter of capturing the sound and embellishing it or carving out some of it so it will sit in just the right sonic space in the mix. Since different microphones are designed to pick up specific frequencies it is a good idea to select the right mic, although when

Dee Rob at Cherokee studios in Los Angeles recorded Mystical Adventures by Jean-Luc-Ponty he used condensers on Rafford Griffin's drums and rolled up the low end with EQ and got a tight punchy sound. The main acoustic problems in rooms, environments and even world class studios are low end standing waves. These can be tamed in various ways. The waves can be reflected in other directions so the waves don’t build up, or you can trap them with a sofit box hanging on the wall. A base trap in the corners of the room can also help. And of course this only really starts to make a sonic difference at high SPL or volume soundUpper frequency axiom ping in the corners of an untreated room can also cause problems. Just go clap your hands in the upper corner near the ceiling of any room with a standard painted drywall wall and you can hear an example of axiom ping; acoustic waves bouncing back and forth over and over until the wave dissipates.

Various thickness depths of acoustic Aurlex foam will treat various frequencies. The thicker the foam the more low end can be absorbed and the thinner the foam the higher frequencies will be absorbed. Room acoustic problems are greatly minimized when listening to a mix at low levels on a great pair of JBL reference monitors. Listening at Low levels will help eliminate early reflections in the control room as well.

Wood just sounds great because it both absorbs and reflects sound and of course different types of wood will very in sonic attributes. So having wood floors or walls can have a good ambience. Making a whole room completely absorbent with no reflective surface is not going to have any sonic character. Try placing instruments near wall surfaces or reflecting off baffle panels for added ambience. Place an amp at a 45 degree angle from a wall then place the mic so it is facing the cone of the speaker as well as the wall, as in the example I described earlier. Record at various distances until you achieve the sound you’re after. A good technique for creating space with a processor would be to pan just the ambience of a signal to the opposite side of the mix so the main signal is on the right and the ambience is on the left. Just route your source signal to a stereo aux and pan.

Here's another idea I had; and you might want to read this a few times so you really get it. What works well with some mixes or individual tracks is to invert the stereo spectrum. Pan the left to right and right to left of your stereo mix. Apply early reflection EFX to the source on right channel. Place in aux send and pan the effect to the left channel, EQ a 10.5 boost or .5 DB at 2.2 slope. The EFX is getting its source from the right and only the EFX is panned to the left. Then pan the EFX out further than the main left source mix. This EQ EFX mix will be placed under or behind the main left channel and panned out farther than the main left mix. Apply reverb EFX to the source on the left aux send

and pan to the right channel, EQ a 10.5 or .5 Boost .3 Db at 2.2 slope. The EFX is getting its source from the left and only the EFX is being panned to the right. Then pan the EFX out farther than the main right mix. This EQ EFX mix will be placed under or behind the main right channel and panned out farther than the main left mix. Then EQ the main left and right channels so the EFX come through if necessary above or hotter than the main dry inverted left and right mix. What you’re left with is the main dry stereo mix inverted and a slight EQ on an early reflection under or behind the left channel and panned farther out so you can hear this EQ EFX mixed well placed under or behind the main Left channel and panned out farther than the main left mix channel. And a slight reverb under or behind the right channel and panned farther out so you can hear This EQ EFX mix and will be placed under or behind the main right channel and panned out farther than the main right mix. So the main mix is inverted and the delay EFX from the right are panned to the left and EQed up. And the reverb EFX from the right are panned to the left and EQed up and panned further out than the dry mix.

We are recording the room, the outdoors, or the environment when we record anything and the sound of the surrounding area will either enhance or detract from the source sound or instruments so analyze the recording environment and treat any undesirable acoustic anomalies. Even foam hanging off a coat hanger surrounding a mic will help a lead vocal recording sound more focused in a very reverberant room. The opportunity to add room ambience can be applied to individual tracks organically or with a processor. A whole mix might sound better in an impulse response of convolution verb but it must be used subtly if applied to an entire mix. Obviously placing reverb on a signal will make it appear further away.

Unless the signal has been routed to an aux send so that the dry and reverb or effect signal can be blended with the dry source. Too much reverb will detract from the punchy in-your-face sound that is so desirable. Capturing just the right amount of room ambiance and acoustic reflection while recording is the goal so you don’t need to add reverb at all. Critical listening well notify you when you are both recording and mixing when enough is enough in terms of ambience. Put head phones on and then move the mic to the position that sounds best or have some one else move the mic for you while they reposition the mic to get that sweet spot position. We don’t always have the luxury of going back so I think it is wise to track everything with no EQ dry clean and with out distortion. With plug-ins you can select any distortion, tap delay, or reverb after you capture the source.

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