VM900 904A 24db filter noisy?

[BetterAngels]

Hi all!

I can't find a more appropriate forum for VM900 specific questions, so I'm asking here:

Is the 904A filter supposed to output so much noise? With no input, as well as at input voltages where a waveform does not start deforming, the 904A filter seems to have very audible noise - which is fine if that is what the real System 55 modules sound like, just maybe I'm patching things incorrectly?

I'm curious to hear other people's experiences.

Thanks!

[UrbanCyborg]

Mark Barton wrote those, so I'd be surprised if they exhibit any noise that the actual analog modules didn't. He's really the expert at that sort of thing. You might drop him a line and see what he says. I also wouldn't be surprised if the original modules didn't have a sometimes noticeable noise floor; Moog modules sounded great, but I'm not sure high S/N was a design criterion.

When you say "no input," do you mean no cable connected, or cable connected, signal level zero? I'd only trust the latter of the two. VM might be reading hash at the module inputs, depending on how the module is constructed.

Reid

[Steve W]

If I crank the Regeneration up to approx. 88% with no input I get a hum. Is that what you are talking about?

Thanks for mentioning this! Some electronic musicians are into making music with zero inputs using hardware (Zero Input Mixing). I have tested some ways of doing this in VM. The 904A sounds like it would be ideal--a nice, mellow filtered sound of self-oscillating nothingness (if it qualifies as Zero Input)!

904A in Voltage Modular - Self-Oscillating Tone - small.png (95.14 KiB) Viewed 3078 times

[BetterAngels]

Mark Barton wrote those, so I'd be surprised if they exhibit any noise that the actual analog modules didn't. He's really the expert at that sort of thing. You might drop him a line and see what he says. I also wouldn't be surprised if the original modules didn't have a sometimes noticeable noise floor; Moog modules sounded great, but I'm not sure high S/N was a design criterion.

When you say "no input," do you mean no cable connected, or cable connected, signal level zero? I'd only trust the latter of the two. VM might be reading hash at the module inputs, depending on how the module is constructed.

Reid

Yes with "no input", I mean no cable connected into the filter: https://gyazo.com/4cee5dfb87d890b1dc5225437c9555d5 (this is a screencapture sharing site)

And yeah if this is simply realistic then that is understandable. Thanks for the response.

[BetterAngels]

If I crank the Regeneration up to approx. 88% with no input I get a hum. Is that what you are talking about?

Thanks for mentioning this! Some electronic musicians are into making music with zero inputs using hardware (Zero Input Mixing). I have tested some ways of doing this in VM. The 904A sounds like it would be ideal--a nice, mellow filtered sound of self-oscillating nothingness (if it qualifies as Zero Input)!


904A in Voltage Modular - Self-Oscillating Tone - small.png

Here is it on my PC: https://gyazo.com/5c542d6b8e24d0124c2da1f690e5e09d (screenshot sharing site)

On frequency range 1, it seems like the filter cuts off practically all of the high frequency noise, but then you are simply cutting that off of the input signal as well. (https://gyazo.com/b8347b62adb2906225cc8d7c99090f3a)

Thanks for the link! I'm gonna take a look at that.

[utdgrant]

I can't find a more appropriate forum for VM900 specific questions, so I'm asking here:

There are two Module sub-forums which would be ideal:

CA/MRB is probably best, as that covers the VM900 series of modules, released under the Cherry Audio / Mark R Barton collaboration,

and MRB, which is more for modules released by MRB himself.

Is the 904A filter supposed to output so much noise? With no input, as well as at input voltages where a waveform does not start deforming, the 904A filter seems to have very audible noise - which is fine if that is what the real System 55 modules sound like, just maybe I'm patching things incorrectly?

I'm curious to hear other people's experiences.

I hear it, too. It's especially clear when you crank up the regeneration into self-oscillation territory.

It's almost certainly the case that MRB is deliberately replicating the behaviour of the hardware module by adding a certain level of noise to the input signal.

On most analogue monosynths (and modulars), you will turn a filter into an oscillator as soon as you go into self-oscillation levels of resonance/feedback/regen. This is because the inherent thermal noise in the circuit gets amplified in an exponential manner until it goes into saturation. With a digital filter, zero input is mathematically 0.0000000000V, and so it doesn't get amplified.

[BetterAngels]

@utdgrant

Yep thanks for the correction. Here's the answer @MRBarton previously gave. If any moderator wants to move my message there, that would be fine.

viewtopic.php?p=8161#p8161