Re: [solved] Re: Live recording
On Thu, 17 Aug 2017, at 08:57, Rodolfo Medina wrote:
> Jeremy Nicoll <jn.ml.dbn.25@letterboxes.org> writes:
> > You do realise that merging files, adjusting balance etc are all possible
> > with sox?
> >
> > One reason I do that sort of thing with sox is that by keeping note of the
> > commands I used to do each stage, I automatically document how I manipulated
> > a set of audio files. Documenting anything done via a GUI as in Audacity is
> > a great deal more difficult.
> >
> > It's worth documenting what you do so that if necessary you can exactly
> > repeat the process at a later date.
>
>
> Thanks... In fact, what you suggest is exactly what I wanted to do but
> didn't
> manage to... In fact, suppose I have two files: piano.wav and voice.wav,
> created by sox in recording piano and voice respectively, simultaneously.
> piano.wav is a stereo file, with the two channels, left and right, inside
> it;
> whereas voice.wav is a monophonic file. When I put them together to
> create the
> final, say, result.wav, I must properly allign them. Now, Audacity makes
> this
> job easy thanks to the graphical possibility of seeing the waving forms
> and
> magnifying them. Instead, with sox, I tried to use the `delay' option
> with no
> success. Maybe can you suggest a better and proper way to do that...?
I've never tried that. The sox mail list is a good place to ask for sox
help.
One thing I'd suggest (since sox is potentially complicated) is that
instead
of trying to use sox with one command that does everything, you try to
do
it in stages. That way you can check that what you get at the end of
each
stage is what you expect. Sox has effects that will tell you about
what is in
a file.
I think first I'd check simply that I could create a file containing
all three
channels, eg by:
sox -V2 --no-clobber -M piano.wav voice.wav threech.wav
The -V2 sets a fairly high level of verbosity; you might need -V3
The --no-clobber prevents sox from overwriting a file. It's easy to get
a command
wrong and accidentally destroy an original file; personally I work on
copies of files
AND use --no-clobber.
-M tells sox to merge the files. You should end up with a 3 channel
file, with the piano
audio on channels 1 and 2 and voice on 3.
If that works (and ironically, Audacity might be an easy way to make
sure) I think
I'd next try to make a file with the voice channel offset from the
others, perhaps
by (guessing again!):
sox -V2 --no-clobber threech.wav delay 0 0 2t voicedelayed.wav
For an experiment, it's worth making the delay substantial, for example
the two
second value (2t) here. It'll be easy to tell if that worked. Later
you can try different
values to get the audio aligned where you need it to be.
(Also note that there's an effect named 'silence' that can be used to
chop unwanted
'silent' or at least quieter than the wanted sound audio out of a track,
so a different
approach that might help would be to make sure that none of the tracks
have much
silence at the start, before you merge them.)
Note that so far, none of the three channels have had their relative
volumes changed.
To do that, and create a stereo file from the three, you'd need to use
the remix effect.
> One more thing: I remember, Jeremy, your suggestion of purchasing a
> multi-channel audio interface, to be preferred to a mixer, and will do in
> future. But do you think that the solution I'm adopting for now:
> different
> files on different single-channel audio cards and then merging them - dou
> you
> think this is a good solution as well...? What difference between this
> cheap
> one and more or less expensive multi channel interface...?
Your current solution is the cheapest I can think of, and no doubt
you'll learn quite a
lot doing this. I'm afraid I've no idea about what's currently
available in cheap audio
interfaces. Reading buyer reviews in eg Amazon is a good way of finding
out what can
and cannot be done with equipment though.
More expensive interfaces will be sold on the assumption that people
using them are
using higher quality equipment, eg decent microphones. As price and
quality of mics
increase you expect to get things like: mics that add little (or barely
audible) noise to a
recording; mics that are more accurate, mics that can better cope with
both quiet and
loud sounds...
Such mics though typically need 'phantom power'. They'd probably be on
'balanced'
audio cables (so 2 wires plus earth/screen per mic), and possibly XLR
connectors...
There comes a point where the box you plug the mics into needs to be
designed for
that.
Then, the signal that comes from a mic is (especially with very
sensitive mics) very
small. It needs to be amplified - which is what microphone
pre-amplifiers do. Cheap
mic pre-amps tend to add noise or ruin the sound from a decent mic...
After that, the amplified sound from each mic needs to be converted from
an analogue
signal to digital. Better quality converters cost more money...
I started recording things (when I was a student) with a cassette
recorder and one cheap
stereo mic. It wasn't until got my first job that I was able to
afford to replace that mic
with a pair of cardioid condenser mics - which needed a special power
supply, which in
my case was basically a box of NiCd batteries totalling 48 volts. It
made a huge difference
to the recordings. Along the way I changed from the original
mains-powered cassette
recorder to battery-operated 2-head and thenn 3-head cassette recorders,
so by the end of
that I could record anywhere, even without mains power. (Of course
that's easy these days
but it wasn't in the 1980s.)
Then there was a long delay before I acquired more mics and a mixer and
a multitrack recorder
(all analogue). In that time I got advice from a local professional
audio hire company, and read
both amateur and pro/broadcast-engineering magazines to learn as much as
I could about what
different pieces of equipment could do, and how different people
approached the problem of
recording different sorts of music. As my interest is mainly in
classical music recording most of
what was in the magazines wasn't very relevant to me, but it all helped
educate me.
There were also recording newsgroups; maybe they still exist, eg
rec.audio.pro
--
Jeremy Nicoll - my opinions are my own.
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