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

[FRO DIDDLY <parispro00@hotmail.com>]

awesome post on noise troubleshooting...especially where to put the EQ in the signal chain-

i found the blurb about midi hard to believe so i googled....its news to me but yes a midi cable can cause a ground buzz in certain sitations....heres a SOS posting going into a little more detail:

ADAT and S/PDIF optical both use fibre-optic cables, giving true galvanic isolation, just like a transformer, so they can never result in ground loops. MIDI inputs also incorporate opto-isolators, so plugging in a MIDI cable should never result in a ground loop. A few MIDI In ports (mostly on budget PC joystick/MIDI adaptors) may omit this circuitry, to save a few pennies, but the most common cause of MIDI ground loops is using an incorrectly wired cable. Avoid five-pin DIN hi-fi cables and use proper MIDI cables, which use only pins four and five for data transfer, and connect the cable screen to pin two only at each end of the cable, but not to the metal shell of the plugs themselves. If a multimeter shows zero resistance between the metal shell of the plugs at each end of a MIDI cable, discard it.






> Date: Thu, 2 Jul 2009 00:32:20 +0200
> Subject: Re: Is RC-50 really noisy? (And other concerns with noise in live rigs?)
> From: moinsound@googlemail.com
> To: loopers-delight@loopers-delight.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
>

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