[Jack-Devel] Cannot combine audio devices with more than 64 channels

[Thomas Brand]

Hi again,

I'd like to throw in a possible alternative for non-resampled audio
transfer via UDP.

jack_audio_send and jack_audio_receive [1]

These programs have several limitations however for a case with two
externally synced interfaces both connected to the same host running JACK
with the same settings it could be worth a try. The number of channels
that can be transimitted depends on the period size.

For two JACK running at -p64, this *should* work:
jack_audio_send --in 196 localhost 1234
jack_audio_receive --out 196 1234
...
196 channels are quite heavy and the send/receive aren't possibly robust
enough so you'd need to see if it works four you or where it breaks.

===
period size: 64 samples (1.333 ms, 256 bytes)
channels (capture): 196
bytes per sample: 4 (32 bit float)
immediate send, no pause or shutdown: no
multi-channel period size: 50176 bytes
message rate: 750.0 messages/s
message length: 51200 bytes
transfer length: 52398 bytes (4.2 % overhead)
/!\ receiver(s) must support message size > 32768
expected network data rate: 314388.0 kbit/s (39.30 MB/s)
/!\ high data rate (OK on localhost), use GigE
===
-> almost 40 MB/s of data moving on localhost, just in one direction.
That's a lot for "just" creating a common audio data domain for both devices.

Good Luck
Thomas

[1] https://github.com/7890/jack_tools/tree/master/audio_rxtx

On Tue, January 24, 2017 17:13, Jörg Müller wrote:
> Thanks for the information.
>
>
> The two MADI FX cards I'm using can be synced via word clock.
>
>
> However, the information needs to be unaltered, no resampling or any
> modification is allowed for our processing. What command line settings do
> I
> have to use to make sure of that? How can I use the official zita-ajbridge
>  or is there some documentation about it?
>
> 2017-01-24 16:36 GMT+01:00 Thomas Brand <tom at trellis.ch>:
>
>
>> On Tue, January 24, 2017 16:27, Thomas Brand wrote:
>>
>>> On Tue, January 24, 2017 09:22, Ralf Mardorf wrote:
>>>
>>>
>>>> On Tue, 24 Jan 2017 07:41:50 +0000, j at jrigg.co.uk wrote:
>>>>
>>>>
>>>>
>>>>> On Mon, Jan 23, 2017 at 05:35:57PM +0000, Fons Adriaensen wrote:
>>>>>
>>>>>
>>>>>
>>>>>> With the official zita-ajbridge you can disable resampling.
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>> Good to know.
>>>>>
>>>>>
>>>>>
>>>>
>>>> Could this be used without word clock, by using a digital interface
>>>> to sync, e.g. S/PDIF? If so, assuming two identical cards would be
>>>> used, would sync be hat good, that each combination of IOs, e.g. a
>>>> channel from one card for the left and of the other card for the
>>>> right channel of a stereo signal, wouldn't cause phasing issues?
>>>>
>>> yes i think that works pretty good (drawing from earlier
>>> experiments). Using S/PDIF just for sync is a cheap alternative to a
>>> "real" wordclock.
>>> One of both interfaces will be slaved to the other and then both
>>> should run the same cycle at the same time (so theoretically no
>>> phasing issues). You just have to manage to shove forth and back the
>>> sample data from/to interface at good enough rate which isn't a
>>> particular problem on
>> localhost
>>> using UDP like zita does. If there is no resampling involved, this
>>> can work for many many channels without hitting the CPU too much.
>>>
>>> Greetings
>>> Thomas
>>>
>>>
>> Even if the interfaces are synchronized with S/PDIF, there will be some
>>  cycles (hopefully a static number) needed to shove data forth and
>> back. This needs to be considered to effectively get synchronous
>> behaviour for input or output to both interfaces.
>>
>>
>>
>> _______________________________________________
>> Jack-Devel mailing list
>> Jack-Devel at lists.jackaudio.org
>> http://lists.jackaudio.org/listinfo.cgi/jack-devel-jackaudio.org
>>
>>
>