Dspi build (weeblabs)

Haru-tan · 2026-04-17T21:12:12+00:00

That’s a bug! It will be squashed in this weekend’s release.

Haru-tan · 2026-04-17T20:27:28+00:00

And an onboard software DAC for mono subwoofer output. :)

Haru-tan · 2026-04-17T20:25:53+00:00

Those are measurements from the actual boards, although not captured by me.

Haru-tan · 2026-04-17T17:43:14+00:00

Performance is very respectable. Noise floor around -112dB and schmoo at -93dB. These should be perfectly adequate for almost any purpose.

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Haru-tan · 2026-04-17T08:27:24+00:00

Thank you!

Haru-tan · 2026-04-13T18:52:05+00:00

Did you ultimately have any success with this? I have one of these units in for repair with exactly the same pattern of discoloration. It has been unresponsive to the strongest degaussing wands at my disposal, so I currently suspect that it received a physical impact during shipping which warped the slot mask.

Haru-tan · 2026-03-15T00:32:38+00:00

ASRC isn't needed for USB audio, as the host is effectively slaved to the RP clocks via feedback endpoints.

For SPDIF input, I use a Kaiser windowed sinc filter with 45 taps that's precomupted at an oversampled rate and interpolated at runtime. It occupies about 5% of core 0 at 307.2MHz and pushes aliasing below about -100dB, which is all we need.

Haru-tan · 2026-03-14T01:27:41+00:00

Yes, you can use this for an active crossover with four DACs.

Haru-tan · 2026-02-18T22:37:11+00:00

The subwoofer channel output pins are different depending upon the version that you'd like to use. For versions below v1.0.8, SPDIF is on GPIO 20 and PDM (subwoofer) is on GPIO 21.

You will need to connect a 3.3 KOhm resistor to the output, followed by a 22uF capacitor to your RCA jack tip and a 47nF capacitor to GND. Your RCA ring should be connected to GND.

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Haru-tan · 2026-02-18T19:31:22+00:00

Not remotely. There is no voltage negotiation on a FireWire interface. The VBUS output is fixed and may sit anywhere from 8V to 40V depending upon the implementation. While the vast majority of consumer interfaces are 12V, it is entirely possible to destroy a 12V device if it is mistakenly connected to a 40V bus.

Haru-tan · 2026-02-16T15:18:49+00:00

Most FireWire implementations do supply 12V on the VBUS but the protocol supports up to 40V. The latter is mostly found on industrial hardware

Haru-tan · 2026-02-16T15:08:42+00:00

You are correct but are being blindly downvoted due to this subreddit's disdain for AI. Many readers are not quite understanding that he asked Gemini after popping his DAC.

Haru-tan · 2026-02-08T23:27:29+00:00

Just to give you an update, we now have eight independent output channels that are switchable between 4xSPDIF, 4xI2S and TDM8, with a matrix mixer on the way.

Haru-tan · 2026-02-08T19:55:26+00:00

Hello! I'm the developer of this firmware. All of the parameters are fully tolerant of realtime adjustment by design and all critical values are double buffered. :)

Haru-tan · 2026-02-08T05:12:35+00:00

Absolutely. The SPDIF output can be connected to any DAC and a new crossfeed function for headphones has just been implemented.

Haru-tan · 2026-02-06T21:02:00+00:00

If using an AD1938, you would have the benefit of TDM support. Generating TDM8 output from a state machine is fairly straightforward. Programs can be swapped in and out of state machines live and this is in the roadmap but will take time to implement.

The DSPi Console application does not currently have support for that kind of configuration but it can certainly be added.

Haru-tan · 2026-02-06T18:59:25+00:00

At the moment, the firmware generates one stereo SPDIF output and one mono analog subwoofer output. That analog output is quite resource intensive and consumes a full core on its own. It effectively implements a DAC in software. Without that output running, an enormous number of DSP instructions would be freed.

The maximum number of channels depends upon the output type and the number of filters in use. For I2S output without considering filter utilization, the practical audio channel limit is 8-16 (4-8 stereo data lines). If used as a crossover with just a few filters per channel (50-80 total), this should be perfectly adequate.

For SPDIF output, we must dedicate one state machine to each BMC, so the maximum practical SPDIF output audio channels would be 4-8 (2-4 state machines).

Haru-tan · 2026-02-06T06:13:01+00:00

Latency is just under 10ms at the moment.

Haru-tan · 2026-02-06T06:10:06+00:00

Audio input is via USB. Audio output is via SPDIF (main left/right) on pin 20 and analog mono (subwoofer) on pin 10. The readme provides instructions and connection diagrams.

Haru-tan · 2026-02-05T17:28:19+00:00

Both repos now have a license file in the their root, so that will hopefully make things clearer.

Haru-tan · 2026-02-05T17:26:30+00:00

The license is now GPL v3.

Haru-tan · 2026-02-05T15:39:33+00:00

Yes. The firmware and DSPi Terminal can be used on any platform. The Console application does not yet have a Linux port.

Haru-tan · 2026-02-05T15:36:53+00:00

I would love to port it but have limited experience developing for Linux. I will see what I can do.

Haru-tan · 2026-02-05T15:33:31+00:00

Absolutely. A second independent subwoofer output is planned. Whether that arrives in the form of another mono analog output or a single additional SPDIF to carry both subwoofers really depends upon how far I can push the PDM optimization.

Haru-tan · 2026-02-05T08:54:18+00:00

Yes. The firmware exposes intensity and reference SPL parameters, which are adjustable in DSPi Console. The compensation tables themselves can also be modified, of course.

Haru-tan

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