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Raspberry DSP
#1
Hi guys, a question ... does the Raspberry use the DSP on board or the processor for signal processing? If it uses the processor, are there latency and jitter problems?
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#2
(04-02-2021, 11:15 AM)ECELO Wrote: Hi guys, a question ... does the Raspberry use the DSP on board or the processor for signal processing? If it uses the processor, are there latency and jitter problems?

What "DSP on board" are you talking about?  I've seen no mention of a DSP on a Raspberry Pi.  As far as I know, a Pi just has an ARM-based SOC.  Do you have a link?

"Latency...problems"?  You're concerned that you will hit play and the music will be delayed by some number of milliseconds?  It's not like there's a lip-sync issue like one has with video.

As to math-induced jitter, who cares?  As far as I know, the math feeds a RAM buffer, which defaults to 128MB in size (you can set it between 8MB and 512MB).
Cheers,
  Miss Sissy Princess
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#3
(04-03-2021, 01:46 PM)Miss Sissy Princess Wrote:
(04-02-2021, 11:15 AM)ECELO Wrote: Hi guys, a question ... does the Raspberry use the DSP on board or the processor for signal processing? If it uses the processor, are there latency and jitter problems?

What "DSP on board" are you talking about?  I've seen no mention of a DSP on a Raspberry Pi.  As far as I know, a Pi just has an ARM-based SOC.  Do you have a link?

"Latency...problems"?  You're concerned that you will hit play and the music will be delayed by some number of milliseconds?  It's not like there's a lip-sync issue like one has with video.

As to math-induced jitter, who cares?  As far as I know, the math feeds a RAM buffer, which defaults to 128MB in size (you can set it between 8MB and 512MB).

Few people know that the Raspberry Pi SoC has an integrated hardware DSP (since the original model), but the APIs are not public and I don't think it has ever been used. The question was: Does Moode use this hardware DSP or does it only work in software?
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#4
Quote:Few people know that the Raspberry Pi SoC has an integrated hardware DSP (since the original model), but the APIs are not public and I don't think it has ever been used. The question was: Does Moode use this hardware DSP or does it only work in software?

Seems to me the question answers itself. No public API === No open-source implementation. This isn't like a communications protocol which can be packet sniffed and subsequently reverse-engineered.

AFAICT, the question of the availability of the SoC-level DSP was first asked on the Raspberry Pi Forum back in 2012 and the answer from the RPF was "we're working on it." The question was asked again in 2013, 2014, 2015,  and 2016 with similar or no response.

Regards,
Kent
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#5
(04-04-2021, 08:34 PM)ECELO Wrote: Few people know that the Raspberry Pi SoC has an integrated hardware DSP (since the original model), but the APIs are not public and I don't think it has ever been used. The question was: Does Moode use this hardware DSP or does it only work in software?

You also asked "If it uses the processor, are there latency and jitter problems,"  the answer to which suggested why it does not matter whether moOde uses the CPU or DSP to do the math.  As long as the samples get into the buffer fast enough that the buffer doesn't empty during playback, it doesn't matter how much math-induced jitter or latency is present on the buffer filling side of the process; the output rate is divorced from the input rate and jitter.  
Cheers,
  Miss Sissy Princess
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#6
(04-04-2021, 11:18 PM)Miss Sissy Princess Wrote:
(04-04-2021, 08:34 PM)ECELO Wrote: Few people know that the Raspberry Pi SoC has an integrated hardware DSP (since the original model), but the APIs are not public and I don't think it has ever been used. The question was: Does Moode use this hardware DSP or does it only work in software?

You also asked "If it uses the processor, are there latency and jitter problems,"  the answer to which suggested why it does not matter whether moOde uses the CPU or DSP to do the math.  As long as the samples get into the buffer fast enough that the buffer doesn't empty during playback, it doesn't matter how much math-induced jitter or latency is present on the buffer filling side of the process; the output rate is divorced from the input rate and jitter.  

Thank you for freeing me from a doubt!
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#7
(04-06-2021, 12:25 PM)ECELO Wrote: Thank you for freeing me from a doubt!

Thank you for informing me about the existence of a previously unknown (to me) DSP in the Raspberry Pi SOCs.  

I wonder if the DSP exists in the BCM2711, which I believe was designed specifically for the Raspberry Pi.  I could see Broadcom deleting the DSP since it's just a waste of real estate on the wafer if they aren't divulging how to use it for the sole customer.
Cheers,
  Miss Sissy Princess
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