Mixing With the Gain Trims
SynAudCon member Rick Chinn suggested an interesting way of optimizing a mixer’s gain staging:
1. Set all the channel faders and master fader to design center.
2. Set up a preliminary mix with the gain trims, making sure the output bus meters read near 0.
3. Fine-tune the mix with the faders.
The claimed advantages are:
—This results in approximately correct gain staging in the mixer and maximum headroom in the input channels.
—Noise theory tells us that for best system noise figure, the first stage wants to get all the gain, and everything afterwards runs at/near unity.
—You can move faders for solos, then line them all up to get back to the basic mix.
—The faders are at their highest-resolution positions.
In other words, you set the input trims by ear to get a good mix, rather than setting them to get a certain signal level. I don’t know whether this would result in optimum gain staging for each channel, but I’m offering it for your consideration.
A disadvantage of this method is that it changes the monitor mix as you tweak the trims.
SETTING GAIN STRUCTURE IN A SOUND SYSTEM
Now let’s examine an entire sound system of these components:
1. Musical instrument
2. Mic
3. Mixer (already covered)
4. Effects devices
5. Compressor/limiters
6. Crossovers
7. Outboard graphic EQs
8. Power amplifiers
I’ll suggest how to adjust each component.
Musical instrument: Electric guitars and keyboards should put out a strong signal to override hum and RFI picked up by the instrument cable. So turn up their volume controls about 3/4 from the top (assuming that allows enough player expression).
The more you can turn up the guitar, the more you can turn down its amp to achieve the same loudness. Turning down the amp reduces its hiss and any guitar-cable hum.
Take care that the level is nominal in each stomp box in a chain. For example, wah-wah pedals boost the signal several dB at certain frequencies, and this can result in distortion if the level feeding the pedal is too high.
Before going on tour, listen to the output of each stomp box in normal use and make sure it’s not more distorted or noisy than it should be.
As always, a noisy output means the input signal is too low, and a distorted output means the input signal is too high.
In general, put signal-boosting devices near the beginning of the chain of boxes, and vice versa. A compressor should go up front because it keeps the signal level high throughout the chain. If you put a compressor at the end of the chain, it will bring up system noise during the release time.
Similarly, a noise gate or volume pedal should be at the end of the chain to reduce noise. The louder a vocalist sings into a mic, the better the signal-to-noise ratio of the mic signal. A loud singer overrides the self-noise of the microphone; a quiet singer or distant-mic’ed singer exposes the mic’s noise floor.