The VCA

Discussions about anything analog, digital, MIDI, synth technology, techniques, theories and more.
AstroDan
Junior Member
Junior Member
Posts: 226
Joined: Sun Jul 24, 2005 12:05 am
Location: Rogers, Ar

The VCA

Post by AstroDan » Mon Jun 02, 2008 1:02 am

Oscillators and filters are a little more obvious, but what is the sonic advantage of a voltage controlled amplifier over digital?

You just don't hear anyone raving about a particular synth's "awesome sounding VCA".
Too futurist to live.

User avatar
hfinn
Expert Member
Expert Member
Posts: 1197
Joined: Fri Dec 10, 2004 3:21 pm
Gear: http://soundcloud.com/heath-finnie
Location: Boston
Contact:

Post by hfinn » Mon Jun 02, 2008 1:08 am

Thats because as far as I know there really isn't much to a VCA. It's just an amplifier.

User avatar
Sir Ruff
Synth Explorer
Synth Explorer
Posts: 3519
Joined: Tue May 09, 2006 11:55 pm
Gear: Two persimmon modulators and a frequency adjudicator.
Band: Ruff in the jungle
Location: Philadelphia

Post by Sir Ruff » Mon Jun 02, 2008 1:16 am

well.... I have heard different things about VCAs... not about them being digital or analogue necessarily, but just their merits.

There was an article on SOS regarding some synth where the reviewer was pretty impressed with a VCA-how it actually kind of shaped the sound depending on how high it was...

(there is a synthesis article dealing specifically with VCAs on SOS as well)

I would imagine, for things like AM or ring mod, which are amplitude based, there might be some sonic difference between analog or digital versions.
Do you even post on vse bro?

User avatar
Synthaholic
Expert Member
Expert Member
Posts: 1206
Joined: Tue Aug 21, 2007 5:43 pm
Gear: Motif XS6, TX802, D-550, A6
Location: NH

Post by Synthaholic » Mon Jun 02, 2008 1:18 am

An analog VCA could add its "color" to the sound of the synth, but since it only controls the output level of the sound, you can't really change that "color" through programming. It's just part of that synth's sound character.

Oscillators and filters have a more noticeable effect on the sound, which is why we talk about them all the time, especially in the analog vs. digital debate.

The equivalent of a VCA in a digital synth is just digital attenuation - signal * level, where level is between 0 (full off) and 1 (full on). Other than possible aliasing if the resolution is low, the digital "A" doesn't affect the sound other than its level.
Two VCO: thanks to the push rods, one can choose several forms of waves at the same time!
(from a Babelfish translation of a Jupiter-6 site)

Yamaha: Motif XS6, TX802 Roland: D-550 Alesis: A6 Andromeda

Mooger5
Expert Member
Expert Member
Posts: 1459
Joined: Tue May 06, 2008 5:11 pm
Location: Lisbon

Post by Mooger5 » Mon Jun 02, 2008 3:19 am

In addition there´s the amplifier´s signal-to-noise ratio: the headroom with which it handles incoming signals without distorting and how dynamically it reacts to envelope cv, ie. how much louder or quieter it sends the signals out and in what manner (if linear or exponential). Read the last chapter (although it´s necessary to read the entire article to understand what it´s about): http://www.synthmuseum.com/magazine/linexpo.html
All those things, sometimes subtle, can make a difference.
Herrare umanum est.

User avatar
V301H
Senior Member
Senior Member
Posts: 754
Joined: Tue Oct 23, 2007 3:58 am
Gear: Fender The Strat, Stratocaster, Jazz Bass Rickenbacker 360-12, 320 Messenger(Mark Farner)
Band: The Characters
Location: New Jersey
Contact:

Post by V301H » Mon Jun 02, 2008 4:30 am

Whether analog or digital the most important aspect of VCA's is how they can be modulated. When considering a synth purchase look at how many modulation sources can be routed to the VCA. Practically every synth allows an Envelope Generator to be applied to the VCA. Most allow LFO mod using a variety of waveforms (the Pro-One is a notable exception). Some synths can modulate the VCA with Velocity or Aftertouch. Occasionally you will find a synth with two VCA's as in the Oberheim Matrix-6. Most Yamaha CS series synths have two VCA's and two of just about everything.
Prophet 5 rev.2, Pro-One, Juno 60, Jupiter 6, Matrix 12, OB8, MS20, Poly 800, CS70M, DX-7, CP35, Casio PX-5S, Hammond C3/M102, Vox Continental/Super Continental, Gibson G101, Farfisa Compact, RMI 300A, Pianet N, Combo Pianet, S770, S760, S50, NS3C

User avatar
neandrewthal
Active Member
Active Member
Posts: 472
Joined: Thu Aug 31, 2006 5:43 am
Location: Ontari-ari-o

Post by neandrewthal » Mon Jun 02, 2008 5:09 am

Most high end modular manufacturers brag about how "clean" their VCA is. So, in that respect the best VCAs would be the ones you never sonically notice at all.
What happens at fondue stays at fondue!

User avatar
cornutt
Moderator
Moderator
Posts: 2117
Joined: Sun Dec 02, 2007 6:03 am
Gear: 6th
Location: Rocket City USA
Contact:

Post by cornutt » Mon Jun 02, 2008 6:08 pm

Yeah, there's a lot less subjectivity in most people's standards for what makes a good VCA, as opposed to, say, a VCF. One thing you do want to see is minimum control voltage feed-through; a rapid change in the control voltage should not produce a "thump" in the output. The VCA should have good dynamic range; distortion in a VCA usually isn't pleasant. And in a polysynth, all of the VCAs need to have the same control voltage respose, or some voices will be louder than others.

It does get more subjective when you get into using the VCA for AM or ring modulation.
Switches, knobs, buttons, LEDs, LCD screens, monitors, keys, mice, jacks, sockets. Now two joysticks!

User avatar
th0mas
Expert Member
Expert Member
Posts: 1349
Joined: Thu Jul 14, 2005 5:27 pm
Gear: oakley tm3030/mopho keys/midibox sid/tr-707/tama techstars/monotron
Band: GRAVITRONIC
Location: Ontario
Contact:

Post by th0mas » Mon Jun 02, 2008 6:42 pm

In a strict comparison to a digial amp, the digital amp will amplify in steps, just as a digital filter filters in steps as you increase the frequency. So there's some zipper-effect on the amplitude.. but your ear is better at smoothing that out so it's less noticeable (plus hardly an issue with high enough resolution, > 8 bits..)

I'm well familiar with the sound as I'm writing a 4-bit synth from scratch and recently coded the amp portion.. 4 bits of amplitude shows noticeable digital steps as you might figure :)

AstroDan
Junior Member
Junior Member
Posts: 226
Joined: Sun Jul 24, 2005 12:05 am
Location: Rogers, Ar

Post by AstroDan » Mon Jun 02, 2008 6:56 pm

cornutt wrote:It does get more subjective when you get into using the VCA for AM or ring modulation.
Yeah, subjective is a good word. I suppose you could also consider quality of capacitors, how much oxygen is in the wiring and the effect of the layout of all the components. I guess if you don't notice the amp - there's no distortion, suitable level, decent bandwidth - then it's a good amp.

I guess the osc's are the players, the filters the cheerleaders and the VCA is the playing field; gotta have a place to play, but who cares what kind of dirt it's made of. :)
Too futurist to live.

GeneralBigbag
Senior Member
Senior Member
Posts: 852
Joined: Thu Jan 19, 2006 10:16 pm
Location: Grad school

Post by GeneralBigbag » Mon Jun 02, 2008 7:47 pm

Correct me if I'm wrong, but doesn't some high end processing equipment (e.g., the 1176) get a lot of love due to the colouration from the VCA?
virb.com/ookpikk

User avatar
kayvon
Supporting Member!
Supporting Member!
Posts: 151
Joined: Tue Dec 20, 2005 3:59 am
Location: London

Post by kayvon » Mon Jun 02, 2008 7:55 pm

cornutt wrote:...distortion in a VCA usually isn't pleasant....
Really? I would've thought some tasty saturation distortion would've been more than welcome.

Isn't that why manufacturers like Studio Electronics sell their discrete VCA upgrade to get a more saturated or in their words 'greasy' sound?

How about a Minimoog VCA, how much of the Mini signal 'magic' is in the VCA I wonder?

User avatar
Analogue Crazy
Active Member
Active Member
Posts: 652
Joined: Sun Apr 23, 2006 5:31 pm
Real name: Rob
Gear: Alesis Andromeda
Korg MS20 Mini
Korg Micro Preset
Korg DS-8
Yamaha Motif 7
Yamaha DX11
Location: Sheffield, South Yorkshire, UK

Post by Analogue Crazy » Mon Jun 02, 2008 8:25 pm

I know i don't shut up about it..the Jupiter-4 has an awsome sounding VCA distortion. It gives sounds more of a dirty 'evil' feel.
A6 Andromeda, MS20 Mini, M500SP, DS-8, Motif 7, DX11,

AstroDan
Junior Member
Junior Member
Posts: 226
Joined: Sun Jul 24, 2005 12:05 am
Location: Rogers, Ar

Post by AstroDan » Mon Jun 02, 2008 8:41 pm

GeneralBigbag wrote:Correct me if I'm wrong, but doesn't some high end processing equipment (e.g., the 1176) get a lot of love due to the colouration from the VCA?
Yes, I've heard a lot of people bypass the compression in the 1176 just to pass signal through it's output transformer. Neve's are famous for their transformer. It's part of many microphones signature sound, as well.
Too futurist to live.

steveman
Active Member
Active Member
Posts: 335
Joined: Thu Oct 05, 2006 4:08 pm

Post by steveman » Mon Jun 02, 2008 9:43 pm

AstroDan wrote:
GeneralBigbag wrote:Correct me if I'm wrong, but doesn't some high end processing equipment (e.g., the 1176) get a lot of love due to the colouration from the VCA?
Yes, I've heard a lot of people bypass the compression in the 1176 just to pass signal through it's output transformer. Neve's are famous for their transformer. It's part of many microphones signature sound, as well.
The 1176 doesn't use a VCA , it's an FET compressor.

All electronic circuits will add colour of some sort but the colouration of a VCA vs the rest of a synth will be minimal. After all those other bits are supposed to generate colour ;)

Bear in mind vintage studio gear was never designed to have colour, they were just designing the best circuits they could at the time, it's just with the passing of time and gear's association with particular recordings that sound becomes desirable - not unlike synths :)

Post Reply