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I am an electrical engineering by training, but I will need to get up-to-speed on basic mixing of noise tracks to create background noise that will hopefully mask out distracting noises from neighbouring apartments. Rather than learning mixing software, I will just learn to use Python and it's toolboxes to examine a composite WAV file that I bought from noisesonline.com, and add in some sound clips from Adobe.

I spsent the last two days trying to read up on tracks and channels so that I can intelligently read up on the Python modules. I think I get it, and reading more will probably not be helpful, based on the variety of ways that I saw to describe the two.

There is one thing that I haven't seen described about the distinction between tracks and channels, but I suspect that it might be true. After filtering, phase shifting, fading, and other effects are independently applied to different track signals, are they irreversibly added together to form a channel signal (say, one of the two stereo channels)? This is the impression I get from the various ways that the distinction has been described.

If so, then a simplified caricature might be a multiple-input multiple-output system, e.g., m=8 input tracks and n=2 output channels. A schematic might show each input connecting to each output, for a total of 16 pathways. Along each pathway would be a box representing the audio effects for that specific input-output pair (fading, reverb, frequency filtering, etc.), which may vary with time, e.g., a sound might go from left to right channel by attenuating with time on the left and growing in time on the right.

With the above "model", each channel would irreversibly sum its 8 inputs. Is that basically the distinguishing feature between track and channel, that signals from the former are irreversibly summed to form a single signal for a given channel?

A small sample of the readings

P.S. When posting this question, this page was suggested, but it didn't clear things up for me. It doesn't address the question of whether track signals are irreversibly added (quantitatively) into a given channel signal. Furthermore, it talks about 5 violins occupying 5 tracks and refers to 5 channels with the same violin sound.

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I think the definition of track and channel is a little looser than what you are describing here, and in the audio world largely comes from the 'tracks' found on a recording medium and 'channels' of a mixing console.

So originally 'tracks' were the distinct bands of space on a recording medium like tape where signals could be. They would usually take one instrument each but could certainly take more when trying to work around the limited tracks at ones disposal. A channel is more a mixing desk (or similar) terminology, ie a pathway where you can send audio and then amplify it (with eg. a mic preamp), potentially eq it and then send it to various other places via VCA's (to send a percentage copy of the signal somewhere else, eg headphones mixes for the musicians) or busses, a bus being pretty similar to it's usual EE definition.

It is usual for a signal, mic or line level, to first go to a mixing desk channel, usually just for applying gain and maybe eq, and providing auxiliary feeds to the musicians headphones, before being sent out to a recording device (historically a tape machine), where it is recorded on one of the recording devices 'tracks'. Usually no irreversible combination of signals is done at this stage, a mic going to a mixers channel will end up on a recording devices track, where the actual audio data is stored.

However it is of course possible to use the mixing desk to send 2 of it's channels to one recording-device track, in which case that track DOES now hold the irreversibly summed original signals.

Similarly, the stereo output from a mixer also combines whatever is put into it, either playback from tracks on a recording device, or raw signals from instruments/mics on individual mixer channels, or other types of mixing desk channel such as groups into a stereo 2-channel signal. This is the irreversibly combined signals of anything you have selected to send down the main (internal) stereo bus of the mixer to it's master (main stereo out) channels, either to monitor recording or construct a mix to save on some other recording medium.

Hopefully that made sense, thats the more 'traditional' view. Modern A/D D/A conversion interfaces muddy the waters slightly as the recording medium and device to capture the signals are all fairly homogenous. A recording interface (general purpose A/D D/A converter with amplification) will have a number of channels (eg. 8 in 8 out) which will feed a number of virtual tracks in some recording software. The tracks are still the logical final destination of audio data in a program such as logic or proTools, the channels are the electrical pathway provided to amplify (maybe process) signals and direct them to a virtual track in audio recording software. Not so helpful is that it's relatively common to say I have an 8 track recording interface because it has 8 useable inputs, so you can record to 8 distinct tracks at once, but really the interface has 8 channels, allowing you to record 8 streams of data separately to 8 audio tracks.

So, what you place on a track is up to you, while recording you can, using hardware or software, request that 2 (or more) electrical channels of audio data be combined into one track, or you can record all your channels on a separate tracks. After recording all the tracks in the audio software they will then usually be combined and sent to outputs 1+2, the main stereo out (though you can split to multiple stereo, or mono outs depending on your purpose), at this stage you have combined your audio tracks (distinct files on disk) into 2 stereo channels for playback or recording via the processing you may have applied with the mixer.

To try and sum up;

Tracks are, in the strict sense, an available destination for a stream of audio data to be recorded, or a stream of audio data on a recording medium to be played back. It may be manipulated, you may have combined multiple audio signals into one track, you may have edited the audio files to be played back (shifted position in time or more elaborate methods) but it is one stream of audio data, incoming or outgoing.

Channels are available pathways on a mixer or similar that can be used to process these audio streams, and set up which audio streams you would like to combine.

Audio will usually end up coming out of a stereo channel, where the result of gain changes, effects and pan in the mixer channel settings will determine what audio the stereo channel will be comprised of.

You can chose to combine audio into one channel at many points in the process, this is used to make better use of limited recording tracks (more traditionally), be able to process combinations of sounds together, or to construct a final mix.

So you can easily combine 2 tracks, record their sum to a spare track, then send that track to a mixer channel to further recombine at the stereo output.

I think you are more or less on the money with how the system works, but the definitions are a little more nuanced, the names were defined with different systems than are common these days, and as it's a field of great commercial interest sometimes the terminology is used rather loosely. Essentially track = holder for audio data, channel = physical/software device for processing and distributing one stream of audio data. Whenever you take two tracks and combine them additively via the channels you send them to you have irreversibly (though of course separation of signals IS potentially possible with advanced techniques) created a new composite signal, to be sent to speakers or recorded on a new track.

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  • @OwenM: Wow. Your answer is gold. I will need to review it a few times. Your acknowledgement of the looseness of it is extremely helpful. It helps me roll with the punches of what I find instead of gritting my teeth trying to find the one true answer. And your high level conceptual distinction will help as I work my way through the terminology. Not there yet, still trying to get PyDub software to play a WAV file. May 17 at 4:50
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    @user2153235 no probs! I probably could have been more succinct.. I had to go back and edit just now as I misused the word track when the proper term is probably channel when talking about mixing desk groups, hopefully that should serve as more evidence that the terminology is a bit loose!
    – OwenM
    May 19 at 23:32

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