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

[rburnett at richieburnett.co.uk]

My understanding is that "FM" synths often decrease the modulation index 
with increasing pitch towards the top of the keyboard to curtail the 
extent of the modulation sidebands.  This is a crude but effective way 
to reduce the amount of high-frequency energy that would otherwise alias 
badly with a relatively low sample rate such as 48kHz.  So, you wouldn't 
necessarily expect the waveshapes in the top few octaves to match those 
lower down the pitch scale.

-Richie,



On 2022-11-28 08:32, Donald Tillman wrote:
>> On Nov 27, 2022, at 5:44 AM, Ingo Debus via Synth-diy 
>> <synth-diy at synth-diy.org> wrote:
>> 
>> 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.
> 
> That waveform has a heavy 10th harmonic going on.
> 
> And for a 2 kHz note, that would be 20 kHz.
> 
>   -- Don
> --
> Donald Tillman, Palo Alto, California
> https://www.till.com
> 
> 
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