MUFF WIGGLER Forum Index
 FAQ & Terms of UseFAQ & Terms Of Use   Wiggler RadioMW Radio   Muff Wiggler TwitterTwitter   Support the site @ PatreonPatreon 
 SearchSearch   RegisterSign up   Log inLog in 
WIGGLING 'LITE' IN GUEST MODE

VCA sound quality?
MUFF WIGGLER Forum Index -> 5U Format Modules  
Author VCA sound quality?
BudgetInfinity
Are all vca’s generally equal when it comes to sound quality?

For instance can a standard vca do cv mixing of audio tracks from a daw without imparting a sound or degrading the sound?
Ranxerox
The short answer to your first question is they can be different.

To your second question, mixing is accomplished by adding multiple audio signals together. VCAs don't do mixing - they control the level of a given signal via another signal (a form of multiplication).

Regarding imparting a sound, yes they can do - whether this amounts to 'degrading' the sound, well that's subjective and also depends on what your audio material is.

The Moog 902 VCA, for example, is technically a bit of a lousy design, but imparts a desirable sound character when processing the oscillator signal which is an integral part of the classic Moog identity. Whether this is also desirable when used to process, say, a classical recording, is much more subjective.
Synthbuilder
All VCAs will distort the sound in some way. As Ranxerox says, this distortion can be good. But for mixing pristine audio from a DAW you probably don't want to be using a VCA at all. Which is why the best automated desks use flying faders (motorised control over the channel fader) or keep it in the digital realm. The cheaper automated desks use THAT 218X VCA chips which for most people are good enough.

So some VCA designs will be better than others for keeping it pristine. Any of the 2164 based VCAs will be OK - I think that's the STG one - and the ones using THAT 218X chips a little better. I don't think anyone has a 5U VCA using a THAT chip but L-1 do a Eurorack THAT based VCA. Mine are pretty hi-fi but probably not as hiss free as the 2164 VCA designs.

Tony
unrecordings
Synthbuilder wrote:
Which is why the best automated desks use flying faders (motorised control over the channel fader)


Christ, that's brought back memories of trying to maintain 48 channels of nasty string driven automation on a vintage Neve. If the fader judders, the solution is... ...Get the mole grips out and bend one of the brackets. Just a tad.

Ah the good old days...

(How to tune an EMT Plate ? Tighten all the screws until just before they go PING!)
BudgetInfinity
I shouldn't have said mixing, I mean't controlling levels going into a mixer. I don't have automation on my mixer so CV control of levels via VCA's would allow me to automate the volume part of the mix (without recording and doing it all in the DAW).
Synthbuilder
unrecordings wrote:
Get the mole grips out and bend one of the brackets. Just a tad.


Happy days.

There was a Yamaha mixer in early 90s that would really screw up if the faders were accidentally flicked. Folks from rival desk companies would sneakily flick the faders at trade shows. So I was told...

Tony
Synthbuilder
BudgetInfinity wrote:
I shouldn't have said mixing, I mean't controlling levels going into a mixer. I don't have automation on my mixer so CV control of levels via VCA's would allow me to automate the volume part of the mix (without recording and doing it all in the DAW).


It's sort of the same thing. In an automated mixing desk the VCA circuit would be internal to the desk. The VCA generally sits in the audio path in front of the channel fader. I remember there were even some midi controlled external VCA banks in racks that could be added to standard consoles via the channel effects send and return loop to allow for VCA automation.

So the thing to do is try it out. Use the VCAs you have and see if you like the result. Even the standard dotcom one will be sufficient for many applications. But if you find it a little noisy, or too characterful, then try a cleaner VCA design like those from L-1, STG and the Oakley DVCA.

It's also worth playing around with the signal levels sent to any VCA you use. Generally you want them as high as possible without causing noticeable distortion. So if the sound is starting to get too dirty lower the signal level at the source. Don't go too low though as this will increase the chance of hearing the hiss/hum that the VCA circuit produces. There's a sweet spot where distortion is low and hiss is negligible.

Tony
Ranxerox
BudgetInfinity wrote:
I shouldn't have said mixing, I mean't controlling levels going into a mixer. I don't have automation on my mixer so CV control of levels via VCA's would allow me to automate the volume part of the mix (without recording and doing it all in the DAW).


If you are just wanting to experiment with VCA mixing, then there's no harm in using modular VCAs for this.

But if you're wanting to do a fully DAW-controlled mixdown with 8 or more tracks, for instance, then you might want to consider a purpose-built automated summing mixer like the sum.mation or the sigma.

If the price of these scares you, then as a cheaper alternative you could track down an old Mackie Ultramix. Apparently it will respond to MIDI CC, although it's designed to run with some proprietary software from 1997 - good luck getting that to work!

Or if you have the space, the patience and the inclination, you could consider locating an actual 90s VCA mixing console like the Allen & Heath GS3V or Soundtracs Solo Logic.

But it's a fairly niche application, to be honest - with a decent multi-channel interface, it would be far easier simply to automate the level mixing of you audio signals within your DAW.
burdij
There are three groups of modular VCAs based on the type of gain control element they use. The first group uses a differential transistor pair with voltage control of the common emitter current source that controls the gain. The second group uses operation transconductance amplifiers such as a CA3080 or the related LM13700. The third group uses a VCA gain cell based on the gain cell invented by David Blackmer, founder of dbx. Common parts in this class are the THAT 2181 and ssm2164 (re-issued by CoolAudio as the v2164).

In order to use a VCA in an automated mixdown application the amplifier needs to have a change in gain that is exponentially related to amplitude to compensate for the ear's logarithmic response to amplitude. The first two types of amplifiers need to have external circuitry to generate this non-linear relationship. The Blackmer gain cell has an inherent exponential change in response built in so it exhibits a gain change in dB/Volt.

A second consideration is the amount of distortion caused by the amplifier to the input signal. The first type has high distortion levels due to the asymmetric signal path. The second type has moderate distortion due to the non-linear nature of the amplifier input. There is a narrow voltage range where the response is somewhat linear but if the amplitude gets too high, the diode nature of the input takes effect and the response becomes non-linear. The third type processes the positive and negative halves of the signal waveform through symmetrical signal paths and can be trimmed for very low distortion levels.

The third type of VCA should give acceptable performance for doing automated mixdown of synthesizer and some non-synthesizer types of music productions. Consider that at the time it was invented, 1971, the Blackmer gain cell was used by mixer manufacturers to produce automated mixdown systems for their analog mixers.
josaka
not sure exactly what effect you are after.. but a decent soundcard(completely controllable in/out levels) and some nice outboard would be a better sounding easier option..
MUFF WIGGLER Forum Index -> 5U Format Modules  
Page 1 of 1
Powered by phpBB © phpBB Group