Propellerhead Forum CV Explanation

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#1
2012-11-22, 18:40
 razingspiral Join Date: Apr 2006 Posts: 72
CV Explanation

Hi,

Got a quick question on a subject I probably ought to know more about - That is CV values when controlling a parameter. I've just picked up the Pulsar unit and after some initial scepticism I realise it can (help) make some pretty awesome sounds. Mostly I just play by ear so found my self a little foggy on this one.

Ok, I use CV all the time and am familiar with the fundamentals. What I'm a little unclear about is what value is (or range of values which are) actually controlling my parameter. I'll try explain what I mean with a simple example.

Pulsar LFO 1 > Combinator Rotary 1 (with 'Ancient of Days' patch - Filter frequency).

Firstly I can set the 'Level' control on the LFO, then there's the rotary on the back CV In, finally there's the position of the paramter itself - in this case Filter Frequency.

The way I understand it is the LFO Level governs the amplitude. The CV In affects the amount of signal 'let in' to the control. And the Frequency knob determines the baseline position of the signal.

So if my LFO (say, sine) Level is set at 50%, the CV In is at 50% and the Filter Freq is at 50% I should expect the Frequency value to modulate at 50% +/- 25%.

Is that right? (scratching head).
#2
2012-11-22, 19:58
 selig Join Date: Jun 2003 Posts: 10,515
Quote:
 Originally Posted by psychobyatch Hi, Got a quick question on a subject I probably ought to know more about - That is CV values when controlling a parameter. I've just picked up the Pulsar unit and after some initial scepticism I realise it can (help) make some pretty awesome sounds. Mostly I just play by ear so found my self a little foggy on this one. Ok, I use CV all the time and am familiar with the fundamentals. What I'm a little unclear about is what value is (or range of values which are) actually controlling my parameter. I'll try explain what I mean with a simple example. Pulsar LFO 1 > Combinator Rotary 1 (with 'Ancient of Days' patch - Filter frequency). Firstly I can set the 'Level' control on the LFO, then there's the rotary on the back CV In, finally there's the position of the paramter itself - in this case Filter Frequency. The way I understand it is the LFO Level governs the amplitude. The CV In affects the amount of signal 'let in' to the control. And the Frequency knob determines the baseline position of the signal. So if my LFO (say, sine) Level is set at 50%, the CV In is at 50% and the Filter Freq is at 50% I should expect the Frequency value to modulate at 50% +/- 25%. Is that right? (scratching head).
That's right in general, but there are a few 'gotchas' in there. Pulsar sends out a CV of 127 when Level is set to 100%, but it takes a setting of 80% to achieve a level of 64 (half) of that. This is because the 'taper' of the Level control is setup for volume in dB, and it behaves exactly like the levels in Thor's MBRB, btw.

So you have to convert from dB to 127 scale to get predictable results from Pulsar. In your example above you'd have to set Pulsar's Level to 80% to get a CV of ±64. Setting the CV Trim knob to 64 will then further reduce the range by half, giving you ±32. Also remember the LFO is bi-polar which is why I say "plus or minus" (±) 32 on the CV value. Use a square wave to measure the full range easily.

If you haven't already checked it out, look into ReVolt as a way to know what values are actually being sent and how the various controls affect the results. :-)
__________________
Giles Reaves, aka 'selig'
Audio Illusionist, Musical Technologist
Selig Audio, LLC
USA
#3
2012-11-22, 23:47
 razingspiral Join Date: Apr 2006 Posts: 72
Thanks! I'll have a look at ReVolt too.
#4
2012-11-23, 01:28
 indwellingfire Join Date: May 2009 Posts: 68
Thanks Giles! I was confounded and fascinated by ReVolt and what it did. I'm beginning to see the light.

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