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Suggestions please for 16-channel 24-bit digital audio recorder
Suggestions please for 16-channel 24-bit digital audio recorder
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Old 11th November 2015, 04:17 PM   #21
psg is offline psg  United States
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Quote:
Originally Posted by fret View Post
I bought a WM8804 eval board too... and it arrived today.... gonna give this a try.
Hey fret ... do keep us apprised of your progress, please!
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Old 16th November 2015, 05:50 PM   #22
tuck1s is offline tuck1s  United Kingdom
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Hi guys, sorry just seen your messages now - I have some progress to report.
Firstly - the Behringer Ultranet signals are definitely just AES3-like (or SPDIF-like) PCM audio.
There are two channels per RJ45 connection, running on the D+ and D- signals.

On my unit, the P16I, there's also DC power available on those connections.
The data rate on each pair is approx 12.2MHz, comprising
32 bits data x 8 channels x 48kHz sampling rate - in other words 1.5 MBytes per second. Two pairs means you have 3.0 MBytes per second of raw data.

The 32 bit 'samples' comprise 24 bits of audio + 8 bits of framing. The framing byte is usually 0x01, but occasionally is 0x09, indicating a 'multiframe'. That's essential for locking on to the correct beginning channel. Effectively the true data rate seen by the WM8804 is like "stereo 192kHz".

The 24 bits of audio are in fact 20-bit, the LS 4 bits on my unit are always zero. Other devices such as X32 might have different ADCs and therefore behave differently.
There is some information on my blog about this: http://tuck1s.blogspot.co.uk/ in need of an update.
For my purposes I wanted to stream in the audio in real-time, and write it to some permanent storage. I settled on an XMOS StartKit as being the ideal thing to play with. You can see more about them here: http://www.xmos.com/products/boards#startkit
These are very low cost, available from Farnell, RS etc.

I've written some code for decoding and storing the signals onto SD card. For the sake of simplicity I'm writing just the MS 16 bits of the signals. Currently I'm streaming in WAV format and it works. I can load the recorded signals into Sonar X1 or Audacity and the audio shows up nicely.

My code's freely available on GitHub here: https://github.com/tuck1s/UltranetReceiver
It's not perfect yet - there are many TODOs marked in the code.
I'm also drafting a PCB to go with it here: https://github.com/tuck1s/UltranetReceiverPCB

Note a few things:
- We don't have 'permission' from Behringer, they will probably tell us it is a proprietary interface. However it's pretty simple to decode with a DSO, and everything done can be done external to the box.
- The SDCard code I have used drives the SD card in 4-bit mode. For commercial use you need to sign up to the SD Card Association which costs at least $1000
- The FATFS code I've used is based on published open source, originally on ELM - Softwares and in the derived work here: https://github.com/xcore/sc_sdcard

If there is enough interest I would consider making PCB kits available, but this will take time..!

Last edited by tuck1s; 16th November 2015 at 06:17 PM.
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Old 20th November 2015, 05:56 PM   #23
tuck1s is offline tuck1s  United Kingdom
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Quote:
Originally Posted by fret View Post
I'm also quite interested in reading the Ultranet stream. The application I have in mind is to extract the current tempo from one of the audio channels which contains a click track, and slave my gear to that via MIDI.

Question for tuck1s: the WM8804 eval. board is only going to read one SPDIF stream, so you can only access 8 of the 16 Ultranet channels at once? (That would be enough for my purpose, but I'm interested in what solutions there are for reading all 16 channels).
Yes, you will need 2x WM8804's if you want to read all 16 channels. The PCB I'm working on will have two, plus an SDcard slot and some other spare I/O pins for connecting up e.g. DACs, realtime clock etc.
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Old 23rd November 2015, 03:07 PM   #24
tuck1s is offline tuck1s  United Kingdom
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When using a MagJack to terminate the RJ45 .. you need a true differential receiver circuit to allow both A and B channels to 'float'.

The AM26LV32 works nicely: http://www.ti.com/lit/ds/slls202e/slls202e.pdf with an R network to bias and scale the differential inputs.
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Old 23rd November 2015, 03:58 PM   #25
tuck1s is offline tuck1s  United Kingdom
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Differential line receiver circuit prototype: .. sounds off again: Differential line receiver for Behringer Ultranet
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Old 13th January 2017, 07:07 PM   #26
charliecola is offline charliecola  Scotland
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I have read countless times throughout many recording forums about the desire and need for a portable simple PCM audio recorder with AES or SPDIF interface (either multichannel or just stereo). There is one made by Sonosax that is so expensive it is inaccessible for most but even that is still bogged down with some analog i/o. There is also a plug on module by Zaxcom but this again is multiple thousands of dollars.

Field recordists all over the world regularly carry a complete recorder with lots of extra ADDA circuitry and weight just to use it's spdif input as a "Bit Bucket".

IMHO the first person to make a simple cost effective product that simply records high resolution AES digital audio streams and nothing else (could even simply plug in to AES xlr port) would help so many others and sell many of such a product.

Last edited by charliecola; 13th January 2017 at 07:12 PM.
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Old 31st March 2017, 04:29 PM   #27
mhelin is offline mhelin
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Haven't check this thread since. Guess XMOS startkit could be used without any SPDIF encoder alone, there's the XMOS audio library with examples for that:

https://www.xmos.com/support/librari...category=Audio

Also regarding the WM8804, it will truncate the output to 20 bits by default in certain conditions, and user should set the WL_MASK bit in S/PDIF register to avoid that. All 24 bits output are needed to gain the 102 dB dynamic range.

Last edited by mhelin; 31st March 2017 at 04:37 PM.
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Old 31st March 2017, 07:18 PM   #28
mhelin is offline mhelin
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Well, there are reports that 192 kHz sample rate is too much for XMOS processor if there is any jitter:

Spdif rx 192kHz - XMOS embedded processors. Heart of XMOS technology, XCore.com

So it's better to use any S/PDIF receiver capable for 192 kHz reception. CS8416 is one of them, and additionally has the differential AES3 / RS422 input support so ypu can go straight from the ethernet jack into this chip:

https://www.cirrus.com/products/cs8416/

Last edited by mhelin; 31st March 2017 at 07:24 PM.
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Old 4th April 2017, 11:15 PM   #29
tuck1s is offline tuck1s  United Kingdom
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Quote:
Originally Posted by charliecola View Post
I have read countless times throughout many recording forums about the desire and need for a portable simple PCM audio recorder with AES or SPDIF interface (either multichannel or just stereo). There is one made by Sonosax that is so expensive it is inaccessible for most but even that is still bogged down with some analog i/o. There is also a plug on module by Zaxcom but this again is multiple thousands of dollars.

Field recordists all over the world regularly carry a complete recorder with lots of extra ADDA circuitry and weight just to use it's spdif input as a "Bit Bucket".

IMHO the first person to make a simple cost effective product that simply records high resolution AES digital audio streams and nothing else (could even simply plug in to AES xlr port) would help so many others and sell many of such a product.
That's interesting. The XMOS CPUs have enough grunt to buffer and write 16 streams to a good quality SD card (e.g. SanDisk Ultra), which suggests a compact and portable solution, perhaps battery-powered, with relatively inexpensive BOM (even if external AES decoding hardware is used).

Mhelin do you know a good source of prototyping boards with CS8416 on them? I see there are eBay versions of 'LJM audio' boards but - if these are pirated - I would rather buy an original.

Last edited by tuck1s; 4th April 2017 at 11:18 PM.
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Old 10th April 2017, 06:22 AM   #30
mhelin is offline mhelin
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Quote:
Originally Posted by tuck1s View Post
Mhelin do you know a good source of prototyping boards with CS8416 on them? I see there are eBay versions of 'LJM audio' boards but - if these are pirated - I would rather buy an original.
Don't know any with full access to all pins, there are DAC kits but it might be difficult to tap to I2S or I2C lines if you want use SW control.

How about the AKM receivers, I just ordered this kit:

AK4113 Digital Receiver Board SPDIF to I2S Converter Softwear Control + LCD | eBay

Wonder which receiver is used on P16-M if any (FPGA maybe)? Why can't XMOS processor decode reliably @192kHz. Maybe XMOS should be replaced by some other processor or FPGA? I'm sure that the cheap Altera kit could do everything needed:
ALTERA FPGA Cyslonell EP2C5T144 Minimum System Learning Development Board AS

Is the clock frequency (50 MHz) too slow, the Opencores SPDIF component suggests 100 MHZ clock for 192 kHz sample rate, but can the 50MHz clock PLL'ed (configured) to generate the 100 MHz clock (I guess).
It's though difficult to code (though XMOS isn't easy either). Too bad there is no S/PDIF receiver for Cypress PSoC's (5 LP for an example) though there is the transmitter so I guess it could be done.

Last edited by mhelin; 10th April 2017 at 06:51 AM.
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