[sdiy] How to design out "usb noise"?

[Mike Bryant]

I'm afraid that doesn't actually work.

If you do everything in 2mS (or any other audio frequency) bursts, you still get repetitive patterns appearing on the memory lines so it still produces audio crap.  You really should do the actual audio processing at 48 or 96kHz, then try to randomise lower frequency actions such as generating envelopes, handling MIDI calls and so on.  I divide the code for these up into 32 tasks, then calculate 31 in a random order, one per each 96kHz timeslot, but always with just the 32nd task being always on the 32nd timeslot which transfers the newly calculated values into the active memory locations all the other DSP processing uses.
________________________________
From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Mattias Rickardsson <mr at analogue.org>
Sent: 08 February 2024 15:22
To: Richie Burnett <rburnett at richieburnett.co.uk>
Cc: Synth DIY <synth-diy at synth-diy.org>
Subject: Re: [sdiy] How to design out "usb noise"?

Den tors 8 feb. 2024 13:59 <rburnett at richieburnett.co.uk<mailto:rburnett at richieburnett.co.uk>> skrev:
... if the main micro is processing audio in
2ms blocks that results in an ugly 500Hz current waveform that is quite
hard to filter out!  You either need a *LOT* of local stored charge or a
big inductor to smooth out the ripple of a 500Hz pulse waveform,
otherwise it's influence starts to spread across the board!

Or you just have to fill your processors to keep them busy at all times. Finally, feature creep is the solution! ;-)

/mr

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