freeDSP-aurora - DSP with 8 I/Os, USB Audio, S/P-DIF, ADAT, Bluetooth and Wifi contro

[dspverden]

This is not an ESD protection, it is the RFI filter you have added.
Anyway, this has to be as close as possible to the connectors.

[dspverden]

@all: Today I have added a little video clip showing you how to make a two-way crossover with dspControl! Making a crossover has never been that easy!

[JLOP]

Hello
Nice project
- is It possible to daisy chain to have say 10 or 12 outputs (4 ways + several subwoofers)
- can It do FIR, if so how many taps maximum and per channel
- is it possible to have single ended outputs

All the best for the project
Jean-Louis

[JayShoe]

Originally Posted by JLOP

- is It possible to daisy chain to have say 10 or 12 outputs (4 ways + several subwoofers)

To add more inputs or outputs you can use the FreeDSP expansion header (1x)(freeDSP Guidelines * freeDSP/WIKI-AND-GENERAL-TOPICS Wiki * GitHub) on the Aurora to connect an additional I/O board. There is a freeDSPx-AnalogIO-x8 (freeDSPx-AnalogIO-x8/GettingStarted.pdf at develop * freeDSP/freeDSPx-AnalogIO-x8 * GitHub) that is pretty much the exact same circuit as the Aurora ADC/DAC. It's the same parts (AK4558 and AK5558) so it would give you another 8in/8out. Or you can use any other freeDSPx add-on board (freeDSP | An Open-Source Low-Budget Audio DSP).

Originally Posted by JLOP

- is it possible to have single ended outputs

Yes, for sure. The Getting Started guide of the freeDSP Aurora (GitHub - freeDSP/freeDSP-aurora: freeDSP ADAU1452 with 8 analog input, 8 analog outputs, S/P-DIF I/O, ADAT I/O, USB Audio Class2, WiFi, Bluetooth) says, "In case of unbalanced sinks leave the negative output unconnected". It also references the inputs by saying, "Unbalanced sources can be connected as well by grounding the negative input".

It's common for balanced inputs and outputs to be "passively" switched to single ended by shorting or ignoring the negative intput/output. Of course the resulting question is whether or not this is the right way to do it. Ultimately it depends on your results. The best way to do it for sure would be to actively convert single ended to balanced in the inputs, and balanced to single ended on the outputs. However, in practice it will still work... And in practice you will get excellent results, as long as the wires are kept short on the single ended signals. They no longer have common mode rejection.

The thing to keep in mind is that balanced signals are usually sent at +4dB and single ended (consumer) signals are usually sent at -10dB. So the getting started guide also suggests that you need to modify the gain settings of the output (in the software) to compensate for the difference.

Originally Posted by dspverden

This is not an ESD protection, it is the RFI filter you have added.

Yeah that makes more sense. RFI filter at the inputs, in a metal grounded case would keep the interference to a minimum inside the case. Right!? So putting it close to the inputs will keep the interference out... In theory.

So I have a question... Can that same RFI filter work on the outputs? Also, can the negative pin of the output be grounded? Should it be? I'm trying to determine if we can use the same part for both inputs and outputs (with the RFI and with or without the grounded negative pin).

I'm working on some other schematics to show XLR inputs/outputs, 1/8 inch (3.5mm), and 1/4 inch. I'm also considering drawling up the schematics for an active input/output setup as well. I figured documenting the recommended configuration is the first step.

[JayShoe]

Raphael, can you confirm whether or not these two connectors would work as a passive input/output connector for RCA or XLR?

[JayShoe]

This quad RCA connector would look like this.



And here is the schematic (unverified).




**** I'm trying to figure out if my quad connector is backwards (Left/Right).

[bcodemz]

This is an awesome project! I'm very excited about this. This is almost exactly what I want to do myself, but you guys did it! I would like to help out with the DSP algorithms at some point.

I'm wondering, have you guys ever thought of making a smaller version of this board, but just 4 channels? I would like to put this in a small active speaker.

[JayShoe]

I'm wondering, have you guys ever thought of making a smaller version of this board, but just 4 channels? I would like to put this in a small active speaker.

I've been doing some serious thought about creating an "Aurora lite" which would have no ADC or DAC parts - just FreeDSP expansion headers so you can add whatever parts you prefer.

In your case about the small active speaker concept there is a nice amp module on the FreeDSP site. Amp2 (freeDSPx AMP x2 - Google Docs) and Amp4 (freeDSPx AMP x4 - Google Docs).

In your case for the small active speaker I don't know if you need the XMOS chip at all. Unless you want the speaker to have USB audio you wouldn't need to solder on that chip at all. You would want the ESP32->ADAU1452 and then whatever expansion board you want.

By the way - the current Aurora model does in fact have a freeDSP expansion header. So if you want to test out any other freeDSP expansion boards (inputs/outpus/amps/etc) then you can test it with the Aurora and then move onto your own custom PCB when you have it figured out. It's a wonderful prototyping tool because it has a really flexible architecture.

[dspverden]

Jay, for RCA connections I would recommend to leave the neg. output open else you may overload the inverter.

[dspverden]

Yesterday I had a short moment for doing some measurements, thus, here are some numbers for you:

DAC: -103dB @ 1kHz, 0dBfs, fs=48kHz
ADC: -101dB @ 1kHz, 0dBfs, fs=48kHz
Latency: 1.125ms (talkthrough ADC->DSP->DAC)