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Agreed it needs slightly more DSP. But you probably had to spend longer avoiding any 1kHz getting onto the analogue output.</div>
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Really depends on your cost structures which is better.</div>
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The Electrosmith guys had constant breakthrough on the early Daisys. Don't know if they've fixed it now or not, but lots of people were complaining about it on their forum.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Richie Burnett <rburnett@richieburnett.co.uk><br>
<b>Sent:</b> 09 February 2024 13:17<br>
<b>To:</b> Mike Bryant <mbryant@futurehorizons.com>; Mattias Rickardsson <mr@analogue.org><br>
<b>Cc:</b> Synth DIY <synth-diy@synth-diy.org><br>
<b>Subject:</b> Re: [sdiy] How to design out "usb noise"?</font>
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<div class="PlainText">It's just a lot more efficient to process audio samples in blocks though,
<br>
even if these blocks are relatively small like 8 samples. Otherwise the <br>
"setup" and "teardown" overhead of each audio processing task is <br>
disproportionately large in order to just process one single audio sample. <br>
Much better to gear up for a particular task (e.g. filtering audio,) then <br>
process a bunch of samples in one run, before suspending that task and then <br>
getting set up for the next task. It "amortises" the setup and teardown <br>
overhead over a bunch of samples.<br>
<br>
For instance my DSP virtual-analogue drum machine (hobby project) <br>
synthesises 1ms of audio for the bass drum, then synthesises 1ms of audio <br>
for the snare drum, then 1ms audio for the clap, etc, until it finally mixes <br>
all of these individual voice buffers into a 1ms stereo output buffer to be <br>
DMA'd out to the DAC. If it had to generate one sample at a time for each <br>
of 16 voices it would not be realisable at all on a low-end DSP.<br>
<br>
-Richie,<br>
<br>
<br>
-----Original Message----- <br>
From: Mike Bryant<br>
Sent: Thursday, February 8, 2024 3:32 PM<br>
To: Mattias Rickardsson ; Richie Burnett<br>
Cc: Synth DIY<br>
Subject: Re: [sdiy] How to design out "usb noise"?<br>
<br>
<br>
I'm afraid that doesn't actually work.<br>
<br>
If you do everything in 2mS (or any other audio frequency) bursts, you still <br>
get repetitive patterns appearing on the memory lines so it still produces <br>
audio crap. You really should do the actual audio processing at 48 or <br>
96kHz, then try to randomise lower frequency actions such as generating <br>
envelopes, handling MIDI calls and so on. I divide the code for these up <br>
into 32 tasks, then calculate 31 in a random order, one per each 96kHz <br>
timeslot, but always with just the 32nd task being always on the 32nd <br>
timeslot which transfers the newly calculated values into the active memory <br>
locations all the other DSP processing uses.<br>
<br>
<br>
From: Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of Mattias <br>
Rickardsson <mr@analogue.org><br>
Sent: 08 February 2024 15:22<br>
To: Richie Burnett <rburnett@richieburnett.co.uk><br>
Cc: Synth DIY <synth-diy@synth-diy.org><br>
Subject: Re: [sdiy] How to design out "usb noise"?<br>
<br>
Den tors 8 feb. 2024 13:59 <rburnett@richieburnett.co.uk> skrev:<br>
... if the main micro is processing audio in<br>
2ms blocks that results in an ugly 500Hz current waveform that is quite<br>
hard to filter out! You either need a *LOT* of local stored charge or a<br>
big inductor to smooth out the ripple of a 500Hz pulse waveform,<br>
otherwise it's influence starts to spread across the board!<br>
<br>
<br>
Or you just have to fill your processors to keep them busy at all times. <br>
Finally, feature creep is the solution! ;-)<br>
<br>
/mr<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
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