Re: Is RC-50 really noisy? (And other concerns with noise in live rigs?)

[Rainer Straschill <moinsound@googlemail.com>]

> - With respect to multiple gear in one live rig with pedals, mixers,
> compressors, drum machines, mics and too many cables all around, how
> have you guys combated the noise floor that creeps in?

Noise creeps in from different sources, they mainly being:
a) components in the chain which generate noise on your signal lines
b) components in the chain which pick up noise from elsewhere (aka EMI)

With that come some suggestions in unordered fashion:

1. "that what Andy calls gain staging"
Generally, noise (of type a) in a device is something independent of
the level of your input signal. However, what we usually find annoying
is not the amount of that noise floor, but more the signal to noise
ratio (SNR - where big means good). We can increase that ratio either
by reducing the noise floor (which may not be possible) or by
increasing the signal level.
Practically, make sure that your full-level signal makes full use of
the headroom for every device in your chain by adjusting the input
level properly.

2. MIDI
MIDI istelf, of course, has nothing to do with your audio signal.
However, MIDI cabling can in a lot of cases generate ground loops.
There is a simple workaround: remove the shield on one end of your
MIDI cable. The signal transmission remains intact, but the hum (which
runs over the shield) can be cured.
Should not be used for overtly long MIDI lines, and it also makes
sense to use MIDI cabling to spec (i.e. twisted pair)

3. dynamic effects
This somehow relates to (1) above. Turn of the output when you don't
have any input signal (i.e. use a gate), and use compressors/limiters
in front of critical devices to increase the signal level you can hit
the device with and thus the SNR.

4. noise and EQs
The most disturbing noise is usually in the region around 7kHz (+/-).
The reason: there's not a high level of wanted signal to mask the
noise, thermal noise (aka the thing we usually have in electronics as
the dominant noise source) is very strong here, and the sensitivity of
the human ear is still very high in that range.
So if you have the need for an EQ in your signal chain where you boost
that frequency range specifically, put it way in front of the signal
chain, so noise generated by the following devices will not be
amplified further. Conversely, if you need to attenuate that range,
put the EQ as far to the end of the chain.
(nb: effects can be swapped freely in case of linear time invariant
devices or linear time variant devices in combination with devices
which "don't do time stuff themselves", like delays. So you can put an
EQ either before or after a delay or modulated delay without any
change, but not before or after a distortion (because that not being
linear).

5. signal chain vs. signal array
Use a mixer, and mute all unused channels. Avoid chained effects
wherever possible.

6. reduce air-bound EMI
keep audio lines away from transformers (especiallly the cheap
transformers). use symmetrical wiring wherever possible.

7. digital domain
If not avoiding this domain completely, stay in the digital domain as
long as possible. Best yet, use a computer in combination with some
decent A/D/A.

Best,

              Rainer