Basic reverb / allpass

Algorithm development and general DSP issues

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veqtor
Posts: 2
Joined: Mon Oct 24, 2011 3:24 am

Basic reverb / allpass

Post by veqtor »

Hi, I'm confused as how to implement a basic reverb on the fv-1.
I want to be able to scale the reverb room size (the allpass delay times) using one of the potentiometers...

The allpass type I want to use is this:

Image

But another strange thing is... I'm having a hard time wrapping my head around the actual sequence, should it be basically:

get input and write it to tap delay reg
get feedback taps and write into acc
add allpass ring feedback into acc
allpass acc (coef1)
allpass acc (coef2)
allpass acc (coef3)
write acc to ouput
lowpass + highpass acc
write acc to allpass ring feedback

I want to use a multi-phase lfo for modulation of the allpass delay times also, can I use the ramp lfo's add the phase offsets and wrap them within pi and then shape them into triangles and then using log to make some kind of pseudo sine shape?
frank
Posts: 1244
Joined: Wed Oct 19, 2005 12:26 pm
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Post by frank »

We actually have special instructions to handle doing an all-pass in 2 instructions. This assumes that the input is in the accumulator already (i.e. from a 'rdax adcl,1.0'):

rda ap1#,kap ; Read output of allpass1 and multiply it by kap
wrap ap1,kap; Write ACC to input of allpass1 and do
; ACC*(kap)+ap1# (ap1# is in LR register)


Result is in the accumulator and could feed another all-pass or get written to the DAC with a 'wrax adcl, 0' type instruction.

I've never tried what you are suggesting with the ramp LFOs so I say give it a try. I'm interested to see the result.
Frank Thomson
Experimental Noize
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