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

[Mike Bryant]

> The highest key waveform looks very different.

That looks to me like the phase of the modulating frequency is different wrt to carrier compared with the other notes.  Don't know if this is a DX-7 thing or just a random phase of the moon thing.

________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Ingo Debus via Synth-diy <synth-diy at synth-diy.org>
Sent: 27 November 2022 13:44
To: synth-diy mailing list <synth-diy at synth-diy.org>
Subject: [sdiy] Frequency modulation vs Phase mod, was: Buchla 295 10-band comb filter topology

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







-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20221127/bcb9996e/attachment.htm>