One of the most important factors in creating great sounding master tapes is the proper optimization of signal levels. Virtually every piece of gear in the studio has either some kind of input level control (usually a knob or slider) or output level control. If you are unfamiliar with the concept of level (or gain) optimization, you might assume that it doesn't really matter at what level you set the output of your guitar or keyboard. If it's not loud enough for you, simply crank up the input fader on the mixer to make it louder. Wrong!
Every knob or slider on your equipment has an optimal range that will yield the best performance and clarity with a minimum amount of noise. Predictably, the optimal range of every input and output varies from device to device. What we want to do is find out where the 'sweet' spots are on each device, and make sure that we stay as close to those points as possible. The benefits include minimal distortion, low noise, and better overall sound. The manufacturers of recording equipment define the 'sweet' spots as nominal level -- representing the best level for regular operation. Nominal level, also referred to as operating level, is engineered high enough to avoid distortion or clipping, and low enough to avoid amplifying residual noise present in the device.
With most pieces of audio gear if the output levels are set too low, then the next piece of equipment in the signal path is required to boost the level in order to bring up the overall volume. Raising the level much past the nominal level has the unwanted side effect of also increasing the volume of the low-level noise on the input device. As a rule of thumb, you will avoid this problem if you set the output levels of instruments, effects, etc. as high as possible. The exception to the rule is when the output level is set so high that the device's input cannot handle the signal and distorts or clips. In this situation you must back off the output level until you hear a clean signal with no distortion.
How do you determine the nominal level of all your gear? If you're like most musicians you've simply leafed through the owner's manuals and missed the sections on setting levels (if they were there to begin with). With a vast majority of recording equipment, the nominal level seems to be at a point about 3/4 of the way up the fader, slider or knob. So without any other information to guide you, if the input level knob goes from 1 to 10, set it to around 7 before making any other adjustments. On mixing boards you will generally have a zero level area, which, coincidentally, is about 3/4 up the fader path.
If all equipment was built identically, your level problems would be over. Hook everything up, set each knob or slider at 3/4, and start recording. Unfortunately, the output levels between external processors, keyboard modules, pre-amps, microphones, etc. can vary wildly. That is why most mixing boards have an additional control, called a mic/line input control or trim control. Its main function is to allow you to keep the channel faders on the board around the zero mark, while giving you the control to lower or raise the incoming signal to allow for differences in output from your sound producing devices.
I generally start out the leveling process by cranking the output of my keyboard modules, effects devices, guitar processors, and tape/CD players to the maximum. On the mixing board, I set the channel trim controls, the channel faders, and the master output faders to around the 3/4 position. I also set any EQ controls flat, or zero.
Next, I'll pop a CD into the CD player, and adjust the level on my power amp to a comfortable listening level, or, at least the level at which I monitor at most frequently. Since the mixing boards' master output is already at the nominal level, I assure myself of a low noise floor. If your mixer has VU meters, now is good time to check and see if they are peaking close to the red zone. The red area signifies the point at which distortion may be introduced into the signal. The key word here is 'may'. Since all mixing boards vary slightly, one manufacturer may allow signals (especially peak signals or transients) to go into the red without introducing distortion, while another may clip when signals barely hit the overload indicators.
I'll caution you at this point that, in my experience, to mix by using your eyes is not a good idea. Sometimes I think that if there were no VU meters at all, we would all be better off because we would be forced to use only our ears and the gray matter between them. Listen! If your VUs are in the red and you hear no distortion, keep pushing the faders. The higher you can go, the more music you will get to hear, with the minimum amount of noise. The only thing the final consumers of your music care about is the sound, not how close you were to keeping the VU at a zero level.
If I hear distorted sound coming from the speakers when playing a CD and everything is set to 3/4, then the adjustment I would make would be to the input trim control, on the channel fed by the CD player. Back it off the maximum until the distorted sound is gone.
Next, I play each keyboard, sound module, and guitar processor in turn. Again, if the sound is distorted or quite low in volume, the first adjustment should be at the channel trim control. Play your keyboards and/or your guitar with some force and with a variety of patches; you want to be sure you will not distort the input channels on the mixer when you are really digging in. Many keyboards and guitar multi-effects boxes ship from the factory with their individual presets somewhat balanced against each other, but often times some presets sound much louder than others. The best adjustment in that case will be to program the preset's master volume at a lower value, leaving the unit's overall volume control set to maximum. In rare cases, you may hear distortion even when you have the mixing board's channel trim at its lowest level. In this situation you have no choice but to lower the input device's master volume until you hear clipping disappears.
Lastly, I'll adjust the effects processors that I have inserted into the signal path using the effects send/return buses on the mixing board. When my processors have input controls, I'll start them off at the 3/4 level, and if they have output controls, I'll set them to maximum output. I also set the master effects send and return levels on the mixing board to 3/4. I then run several different sounds (guitar, bass, drums) through the effects processor at various levels using the effects send knob on the individual channels. Listening is very critical at this stage; if you hear distortion when you turn the channel effects send knob up past halfway, you may have to lower the master effects send a bit until you get clean results. If you find yourself lowering the master effects send more than halfway, you should make any further adjustments by lowering the effects processor's input control. If you still can't get a clean signal, lower the master effects return slightly to achieve clarity.
With some older or budget effects processors, excessive noise can be a problem, especially when the device is not being used in a particular musical passage. In this situation, with no music playing, I lower the master effects return until the noise disappears or is at an acceptably low level.
Listening through the master mix output with headphones with no music playing is a great way to monitor for any excessive noise throughout your system. You can solo each channel to determine which device is adding noise just by being turned on. You can make small adjustments at the input channel's trim control to try to squelch the noise, but if it causes you to have to crank the channel fader to maximum when the device is playing, then I would raise the trim back to its original position and try lowering the output slightly on the noisy device. I always tend to blame the effects processors first for adding noise. Noisy guitar processors are next. Remember that a cranked preamp can sound great. It may be better to insert a noise gate or a noise reduction unit between the processor and the mixing board instead of tampering with the input trim.
Remember that attempting to maintain the channel faders of your mixing board around the zero level mark is designed to give you more headroom. Headroom, in this case, is that last one quarter of the fader's path that you can use to boost the signal when mixing. Adjustments like equaliztion will also need to use a bit of that headroom. For example, if you want to boost the bass on your guitar track, the overall level will be louder, which reduces the amount of headroom. When all your headroom is used up, unless you are Spinal Tap, you may not be able to 'push it to 11', to get more sound.
A special note about digital recorders: when adjusting levels for DAT decks or digital multi-track machines, keep in mind that zero on the meters really means zero. The digital grunge that will be recorded onto tape when you exceed zero is simply nasty, odd harmonics that no distortion-lover could tolerate. Carefully listening back to your tracks or mix should ensure that the square-waved spew is identified and eliminated. Unfortunately, the only way to fix the problem is re-recording the part, or re-mixing the song.
The message should be ringing through loud and clear by now. Instead of just keeping an eye on your signal levels, try keeping your ears tuned into hiss, rumble, distortion, clipping, and sounds that go bump in the night. When you hear something that just doesn't sound quite right, stop and readjust the input and output controls until you achieve clarity. Even with a modest home studio setup you should be able to deliver a very clean master tape to a duplicator, and, with luck, you may make a long-term impact on your income levels.
Dan McAvinchey is a guitarist and composer living in Raleigh, NC.
He believes every musician or composer has the power to write, record and release their own music.
His 1997 CD release on Guitar Nine was entitled "Guitar Haus".
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