[sdiy] Frequency modulation vs Phase mod, was: Buchla 295 10-band comb filter topology

[Ian Fritz]

Ingo --

Many thanks for doing this! Your result is similar to what I got using a 
"DX7" plugin. There, also, there were strong signs of the instrument's 
LP filter.

If the signal were PM, the modulation amount would change by a factor of 
two for every octave. This would be quite obvious, I think.

Ian


On 11/27/2022 6:44 AM, Ingo Debus via Synth-diy wrote:

> So here we go. I measured the output of my DX7, for all six C keys of 
> its keyboard. It was set to Init Voice, with the following modifications:
> Algorithm 1
> Op1 Output Level 99
> Op2 Output Level 99
> Op3…Op6 Output Level 0
> Keyboard Scaling all 0
> 
> We see that the waveforms of all keys except the highest key look 
> similar, but not exactly the same. The highest key waveform looks very 
> different. Maybe this is just a lowpass filter effect of the DX7 
> (certainly not of the scope, this is a 60 MHz scope). The frequency of 
> the highest key is about 2 kHz.
> 
> If anyone wants me to measure something else, let me know!
> 
> Ingo
> 
> 
> 
> 
> 
> 
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