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Cronus - It's about time.

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M

MatthewF

Member
Joined 2010
Hi all,

Apologies if this is a silly question (I have a feeling it might be..)

Does the Hermes-BBB / Cronus combo support bi-directional audio i.e. PCM streams from BBB to DAC and also, simultaneously, from ADC into BBB? (The ADC in question would be clocked from the Cronus, so synchronous with everything else.)

I'm looking to implement good quality recording and playback with the BBB. As I'm not familiar with the re-clocking technology involved, I can't quite figure out if I2S audio would successfully pass from ADC to BBB (i.e. travel in the opposite direction to what everyone else seems to be doing!)

Best,

Matthew
 
M

MatthewF

Member
Joined 2010
Thanks for your reply Miero!

In that case I wonder if there would be some value in using a modified Hermes to provide isolation for two I2S inputs and two I2S outputs (changing half of the isolators on Hermes-BBB as you described below).

I could then could then run my output channels through Cronus as per usual, and use the mclk from Cronus to clock my ADC. The I2S output form the ADC would bypass Cronus and directly feed the modified isolators on Hermes-BBB. (Hopefully the ADC's output would be clean enough that no re-clocking would be necessary.)

Does that seem like a plausible idea? I note from your driver documentation that simultaneous record and playback of multiple I2S signals could be achieved by setting the serconfig parameter to "IIRR". Have I understood that correctly?

Thanks again for your help!

Best,

Matthew
 
M

miero

Member
Joined 2011
Output of Cronus matches Buffalo 3 pin mapping (check its documentation).

Input side of Cronus:
- 1 DCK_IN (bitclock)
- 2 GND
- 3 D1_IN
- 4 GND
- 5 D2_IN
- 6 GND
- 7 D3_IN
- 8 GND
- 9 D4_IN
- 10 GND
- 11 D5_IN
- 12 GND
- 13 D6_IN
- 14 GND
- 15 CS (input pin - clock select)
- 16 GND
- 17 MCK (output pin - actual master clock after division (J1 or J2) or direct (J3))
- 18 GND
- 19 3.3V
- 20 3.3V
 
S

sureshm

Member
Joined 2007
Russ, can I please check if I have understood this correctly. With a Amanero-Hermes-Cronus Combo, the source feeding the Amanero has little influence on the final sound as the i2s going in to the DAC is re-clocked and isolated using a clean power supply? Therefore all the USB products out there that attempt to clean the USB signal/power (Jitterbug, ISO Regen, etc) won't be that effective? A simple rpi3, despite its various flaws, is sufficient to get very good sound as a source feeding the Amanero-Hermes-Cronus?
 
francolargo

francolargo

Member
Joined 2007
Paid Member
MatthewF said:
I see, thanks for the info!

I think I'll look into developing my own bi-directional isolator board, and will hopefully still be able to use Cronus as masterclock and to re-clock the I2S output from the BBB.

Cheers!

Matthew
Click to expand...

Any progress on this, @MatthewF? Do you need the BBB to adapt to various input sampling frequencies, or will one input frequency suffice? If one frequency will do, the USB inputs to BBB work well as a client for streaming material up to 96kHz. SoX on the BBB will truck the USB through to ALSA, from which nicely-clocked I2S exits via the isolators and on to the DAC. I could give you some suggestions on working syntax for SoX and optimal BBB configurations...
 
francolargo

francolargo

Member
Joined 2007
Paid Member
miero said:
Warning: BBB is not fast enough for SoX resampling on a better quality than low!
Click to expand...

True - excellent point! To use SoX for USB streams you should decide what sampling rate SoX will use (96k or less) and perform any resampling on the supply side. For good quality filters (such as HQPlayer...) that resampling will require much more CPU than the BBB can muster. However, at 44 and 48kHz, SoX can run IIR or basic FIR filters using the BBB.

In my system, all sources using the USB input are fixed at 48kHz and any resampling happens in those upstream appliances. For these signals, the USB input pathway works great! ;) ...and when the native freq. of the program material is 48k, the sound quality is impressive.

SoX has the lowest latency of the different options I tried for passing audio from video through to the DAC. Here is a command line example:

Without filters the buffer can probably be 1024:

Code: 
chrt -f 45 sox --buffer 1024 -r 48000 -c 2 -t alsa hw:1,0 -t alsa hw:0,0

If I add a small FIR filter for mid freq. room modes, then a buffer of 2048 is better:

Code: 
chrt -f 45 sox --buffer 2048 -r 48000 -c 2 -t alsa hw:1,0 -t alsa plug:filter1 fir /usr/filter/fir2peak48.txt vol 0dB 0.02

To run an LADSPA filter, the syntax would look something like this - ending with the filter parameters:

Code: 
chrt -f 45 sox --buffer 1024 -r 48000 -c 2 -t alsa hw:1,0 -t alsa plug:filter1 ladspa ACDf 21 1 0 240 0.707 0 0 ladspa ACDf 21 1 0 240 0.707 0 0

I experimented with multiple SoX commands to create a speaker crossover but it was very tricky to time-align the different channels. ...not good for sound "imaging".

Cheers,

Frank
 
Last edited:
Russ White

Russ White

Member
Joined 2005
twistedpearaudio.com
sureshm said:
Russ, can I please check if I have understood this correctly. With a Amanero-Hermes-Cronus Combo, the source feeding the Amanero has little influence on the final sound as the i2s going in to the DAC is re-clocked and isolated using a clean power supply? Therefore all the USB products out there that attempt to clean the USB signal/power (Jitterbug, ISO Regen, etc) won't be that effective? A simple rpi3, despite its various flaws, is sufficient to get very good sound as a source feeding the Amanero-Hermes-Cronus?
Click to expand...

That is correct. :)
 
francolargo

francolargo

Member
Joined 2007
Paid Member
francolargo said:
To use SoX for USB streams you should decide what sampling rate SoX will use (96k or less) and perform any resampling on the supply side.
Click to expand...

I should have mentioned that (obviously) you can kill and restart SoX using a different sample rate if your different USB sources can't resample. Its just that SoX won't adapt on the fly without performing linear interpolation. Sometimes that's better than nothing! :D
 
Russ White

Russ White

Member
Joined 2005
twistedpearaudio.com

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