Minimum Open Loop Delay

Hardware questions and issues with the FV-1

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Chris Graham
Posts: 2
Joined: Mon Dec 09, 2013 7:51 am

Minimum Open Loop Delay

Post by Chris Graham »

I've searched the specs and forum for this information without finding it so I'm asking here.

I want to experiment with a sort of Karplus system were the delay is supplied by a Spin chip but with other non-digital processing in the feedback loop but external to the Spin chip. Therefore the loop cycle time will include the conversion time of the ADC and DAC plus the variable digital delay of some algorithm in the chip plus any delay in the external analog circuit.

What I want to know is the time that the ADC and DAC conversion times will add to the loop as this will set the minimum loop time. Ideally I'd like to be able to vary the total delay in a range of about 1 to 2 ms and preferably less, up to about 30 ms.

I understand the ADC and ADC are sigma delta types which implies of group delay of a few ms. If this is too much the spin chip may not suit my purposes and I'll need a DSP with a different type (external) of ADC/DAC, of the type intended for servo control.

Can anyone tell me what the group delay of the spin's ADC and DAC?

Have any of you experimented with what I'm trying to do? i.e. A hybrid feedback loop with a digital delay combined with analog elements in the loop.
slacker
Posts: 116
Joined: Tue Feb 01, 2011 1:13 pm

Post by slacker »

I've measured one of my pedals with the FV-1 simply reading the ADC and then writing it to the DAC and got a couple of ms delay. That would have included any slight delay/phase shift caused by the analogue parts of the circuit but I'd imagine they're insignificant. I'll see if I can do another test on just the FV-1.

I haven't attempted any Karpus stuff, but I've played about with using the FV-1 as a delay line with an analogue feedback loop and wet dry mixing. Works nicely with analogue filters in the loop.
Chris Graham
Posts: 2
Joined: Mon Dec 09, 2013 7:51 am

Post by Chris Graham »

That sound promising. Thanks for the information. I'll order a Spin development system and try it.

My goal is to develop an instrument that uses commuted waveguide synthesis (i.e. by Julius Smith). In his design there is a waveguide, a low pass filter, and a nonlinear element, all digital, in a closed loop that resonates to produce sound. The nonlinear element could for example include a model of a wind instrument mouthpiece. In my case I want to use a digital waveguide so the length can be easily changed, but have the nonlinear elements including a "user interaction device" be analog. I prototyped this on a computer and it was cool, but the ADC/DAC delay of the sound card limited the frequency range. The Spin chip looks like an easy way to try a better implementation in hardware.
Sandrine
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Joined: Thu Mar 12, 2015 10:19 am
Location: BC Canada
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Site?

Post by Sandrine »

Wow Chris that sounds cool! I just made a tiny synth and a distortion module that both have similar properties. I know it's been a while, but do you have a site?
Is there a latin word for "Stage Fright"?
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