Re: Recording specific channels

["Michael Cottle, (David)" <D.Cottle@xxxxxxxx>]

 

Thanks for responding. It might be helpful to describe our goals. We are recording 4 spaces of a music building 24/7 using stereo pairs. These files are then used by students, faculty, or staff to listen to rehearsals, create audition materials, or edit concerts. We’ve been doing this for nearly 12 years (using Audio Companion, Amadeus Pro, but currently Logic Pro). Logic is just a shell we use (because it has a nice interface) to write the CAF files, then we use SoX to split them up every hour. We also use SoX to discard silent files. The problem is, Logic can be flakey, so we are investigating SoX as the recording device also. I think I solved my initial issue:

 

I’m currently experimenting with a Focusrite Clarett which has 8 analog and 10 digital inputs.

 

rec test.aif

 

Records all 18 channels in order. When I open that in Amadeus Pro it correctly recognizes it as 9 stereo channels. (I send test tones to 1 and 3 that are beeping at 1 hz and 5 hz). But this creates is more channels than we need.

 

rec -c 2 test.aif

 

Records the first two channels.

 

rec -c 8 test.aif

 

Records the first 8 channels. I don’t do anything differently to the interface.

 

I have then successfully used remix to split up the files into stereo tracks (the end goal). I didn’t think remix could be used when recording, just with existing files. But I just tried:

 

rec -c test.aif remix 3 4

 

And that recorded just tracks 3 and 4, which was my original question.

 

I then opened two terminal windows and recorded tracks 1 and 2 using one instance of sox, then 3 and 4 with the other. That also worked, which was likewise my original goal. But now the question is, am I going about it incorrectly and taxing the system or sox using remix during the recording process? It is handy to have all the separate CAF files as stereo pairs (for each room), but would it be more efficient to record all 8 channels to a single file, then split them up using SoX and remix?

 

 

 

5/11/24, 04:33, "Jeremy Nicoll - ml sox users" <jn.ml.sxu.88@xxxxxxxxxxxxxxxxxxxx>:

 

On 2024-05-10 23:56, Michael Cottle, (David) wrote:

> I need to record specific channels from a multi-channel interface.

I would GUESS that how you do this depends on whether the audio
interface(s)
always send all channels of audio, or only those you choose on the
inteface
itself.

Then the file (or stream) of audio might contain header info saying (to
sox)
how many channels of data are being sent.  Or it might not in which case
you
would HAVE TO TELL sox what is coming in.


According to the so manual, sox can be told via   -c n    eg -c 4   that
the
incoming audio contains that number of channels ... so your example of
-c 2
doesn't seem right to me unless the interface was ONLY SENDING 2
channels of
audio.


If eg you have an 8 channel interface configured only to send 5 channels
I've
no idea whether sox would know there's 5, or know there could have been
8,
or be sent 8, 3 of which are silent, or have no idea at all.  Presumably
the
manuals for the interfaces will tell you...  Alternatively you could use
soxi
to find out what is in the file according to its headers.


If sox is being sent, say, 5 channels of audio, you use the "remix"
effect
to map selected input channels onto the desired output channels.


--
Jeremy Nicoll - my opinions are my own


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