Re: LF: Octo-soundcard for the Raspi, another question

[Paul Nicholson <vlf0403@abelian.org>]

Stefan wrote:

> i did expect that @raw3 has the same format as @raw2
> and that the only difference is the changed samplerate.

All the vt programs write float8 to their output stream
(buffer, pipe, file, network) regardless of the input
format.

The only exception is vtwrite which writes to its signal
database in the format of its input stream.

float8 is usually the best to use, certainly for pipes
and buffers.  For saving to disk you might want f4 to
save space, or maybe i4 or i2 if you can be reasonably
sure of the dynamic range (these are clip-able formats).

> But what if the vtcat stage would be not obsolete for
> some reasons, how could i change the @raw3 format into
> ,i2 again?

In that case

 vtcat @raw:1,2,3 @raw2,i2
 vtresample -r24000 @raw2 @raw3,i2

will do that.   Check with

 vtstat @raw3

to see that it is int2 format.

> I tried vtresample -r24000 @raw2 @raw3,i2 but the
> the process aborts,

Make sure you haven't got another process writing to @raw2
or @raw3 at the same time, maybe one you started earlier
and put in background with -B option.  vtps might help.

If you can shape the PPS and run vttime, you can reduce the
disk space because you don't need to record the PPS channel.

For vttime to work, the Pi clock will have to be set within
a 100mS or so.   The Pi has no built-in RTC and if you're
running remotely you'll have to hook up the GPS to a serial
or USB port and install gpsd and ntpd.  Configure nptd to use
the GPS as a stratum zero time source.

--
Paul Nicholson
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