Multi Channel Audio Widget 4ch

[ben Sharp]

HI all,
         I am very interesting in designing / helping design a multi / channel DAC version of Audio widget.   I would like the groups thoughts with regards firmware support and the hardware. The use for this would be for speaker equalization specifically the for the Linkwitz labs pluto / Lx mini. I have been working on the cross over using Jackd on Linux and have it working well but am struggling find decent quality 4ch DACS. I have used the WM8741 on various other projects would be looking to use this again either 4 in mono mode of 2x DACS so for the 4 channels.
I am electronics engineer with a love of music as such i have no problem doing the hardware design and sharing it if any one is interested. I however don't have experience with this MCU and my knowledge of c programming is passable at best hence i am reaching out to the group for thoughts this specifically the following :-

1) has this been done before?

2) is it possible with the current MCU? I think it only has 1x I2S port

3) implementation firmware , idea of work required?

I look forward to hearing from some of you.

Best Regards
Ben. 

[Børge Strand-Bergesen]

Hi Ben, 

It's an interesting project! 

The main challenge is in your 2nd question. The MCU really only has one I2S out and one I2S in. A potential workaround (which would be needed for proper DSD support) is to use the digital filter bypass lines of the DAC chip. Those typically have one data line for L and another for R. The MCU has a few more USARTS and SPIs which may or may not be put to use there. If so, the main programming effort will be to run the MCU IO in a synchronized way. 

Rewriting the USB descriptors for 4 channels and porting the internal buffer logic will be time consuming but not extremely hard. 

An alternative to connecting DAC data pins directly to MCU IO is to use a small FPGA or CPLD. The IO module used by the DAC for I2S can be expanded to support some homebrew formats which can then be expanded in the CPLD. With proper setup the MCU can hold the boot image of a small programmable device. 

Best,

Børge

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[ben Sharp]

Hi Børge,
            Thanks for quick response, I feared this might be the case, the FPGA or CPLD route is quite interesting, I guess a 3rd option would be to port to the code to a different MCU?. How tied to hardware is code with regards hardware and peripheral library's etc?   I know a few people who use a lot of TI STM32F series chips and i have experience with the STM32F407.  Thoughts most welcome.

Best regards
Ben.

[George Boudreau]

Hi B#, Borge.

Another method is to use the Audio-Widget and feed an audio DSP such as the Analog Devices ADAU1701 (or better).  This device supports either internal DAC (less than stellar) but also exports to 2 x I2S bus to feed external DACs.  You would use the internal DSP routines to filter and route data to each DAC.  A single DAC would support a 2 channel crossover and you could do whatever equalization in the DPS code.

The Audio-Widget would act as the input to the DSP and the DSP would do the heavy lifting and then feed a pair of DAC. 

I have used this method years ago but got sidetracked and never finished it. There are commercial DSP cards kicking around that will take I2S from boards like the Audio-Widget.  Reinvent the wheel,.. maybe it is time to turn out an open source version of the concept.

$0.02 opinion.

George

[Hobbit13]

Hi All, 

It's an old topic, but still relevant to me. I've been using the AudioWidget for years with great pleasure. It's driving the front channels of a Philips SACD1000 (heavily modded!) 

I'm thinking of ways to put the other channels in use as wel:

a) have one I2S feed only containing the left channel and one containing the right channel. The output of the stereo dac chips can be bridged to improve channel separation

b) have one I2S feed with left channel and left channel inverted, and one I2S feed with right channel and right channel inverted. Right channel of the stereo DAC will drive the HOT XLR pin and left channel of the stereo DAC will drive the COLD XLR pin to create a fully differential output. 

Would it be possible to double the sample rate inside the AVR32 and use some logic ICs to send one word the first DAC and the next word to the second DAC? (and divide the master clock by two).

The AVR32 would then need to invert the audio signal for every other sample. (to achieve goal b) ) 

Without any changes in the AVR firmware, goal a) should be doable with similar logic. This is done in the Marantz SA14, see page 1-9/1-10 of the service manual:

https://www.manualslib.com/manual/1411209/Marantz-Sa14.html?page=8#manual

Any thoughts on how to achieve objective b)  using the Audio Widget?

Cheers

Frodo Muijzer

Op dinsdag 29 augustus 2017 om 19:43:33 UTC+2 schreef George Boudreau:

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[FC CRSYSTEMS]

Hello everybody, I was being looking for a 6h Usb Audio DAC by the last 6 months and i find an github rebo were the author shares the code of their funtional prototype, it uses anstm32f4 07/11 . Then I bought 4 boards of this, and PCM (Texas Ins) Dac Boards with the PCM5102, when I received these from aliexpress i tried to clonate the proyect, and it worked really fine. But it only gives 2ch for usb Port and it doesn't works at the sametime pluged on a same multiport usb hub. My limitation is that my principal computer is an Lenovo laptop that only has one usb port, and if I would like to have the 6ch, I need extricly 3 ports.

The repos i tryied is this: https://github.com/har-in-air/STM32F411_USB_AUDIO_DAC

that it is consecuence based on this other for an diferent stm32 discovery board: https://github.com/dragonman225/stm32f469-usbaudio

this other link is were i publish resume of my advanges in my search by the web: https://drive.google.com/file/d/1ot6i8j9FMeHqiNm07WdSk0vRuoxhXNGE/view?usp=sharing

[MirandaBish]

The Marantz SA-14 instructions are fairly extensive and comprehensive . They cover everything from the installation procedure to the player's sophisticated features. They were very helpful in learning the many audio formats offered and how to optimise the settings. Each step is well described, with pictures when appropriate. Even if you are unfamiliar with audio equipment, you should be able to read the manuals with ease. Marantz did an excellent job of making them user-friendly .Such as you can see at this site https://marantz.manymanuals.com/cd-players/sa-14 

воскресенье, 23 октября 2022 г. в 09:19:46 UTC+3, faustino...@gmail.com: