On Thu, 17 Aug 2017, at 08:57, Rodolfo Medina wrote: > Jeremy Nicoll <jn.ml.dbn...@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.
