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Post by Deleted on Mar 26, 2018 0:57:16 GMT
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Post by Boomer on Mar 26, 2018 2:12:04 GMT
Yes, a similar technique is used in processing for AM stereo as well. Left and right audio is passed through a matrix to get left + right (mid) and left - right (side). The short answer is, mid-side processing makes sure that if a sound would be in one channel only for a period of time, like those old Beatles stereo records from the late 1960s, the mono signal still plays at full volume through a mono radio, instead of half as loud. M/S is also in mp3 encoding, to more efficiently compress stereo at lower bit rates, if you set the encoding for mid/side. As I remember, the mid, mono signal gets the most bits, the side, with the stereo difference information needs a lower bit stream, so most of it goes to the mono. You'll have to try it on a World Round Radio show soon..  Boomer |
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Post by Deleted on Mar 26, 2018 2:25:03 GMT
Good Knowledge Bank in Boomer's Head
Boomer tells Carl something he had never heard about: "M/S is also in mp3 encoding, to more efficiently compress stereo at lower bit rates."
That is a chunk of knowledge I've never run across! Probably because I have concentrated mainly on mono mp3 because of being mostly a voice station.
During a few years when I carried a lot of classical concerts I did run stereo, but it was the common variety that was selectable in my Audio Player chain.
I even once tried to think of a way of setting up a pair of M/S channels, but the software didn't support doing it in the way I wanted to do it.
M/S is the perfect compromise because it keeps mono material in mono but passes full stereo if the recording contains stereo.
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Post by Boomer on Mar 29, 2018 4:23:29 GMT
The MatrixI did a little more reading on M/S mp3 encoding, and it's more efficient than separate tracks for left and right, and depending on what guide I read, it might be part of the 'joint stereo' specification. Mid/side is used internally in the mp3 itself, but it's changed from and to regular stereo at the input and output of the mp3. I'd like to know if there's an encoder/decoder that can take raw mid/side audio and record it without the matrix process. That way you could have a center channel mic go to a mid input, and the cross field stereo pickups go to side. That way at the output you could use the mono, or mix in as much of the side channel as needed and play with the sound, with complete control of each stream and the matrix, all that without the mid and side being mixed together until your final project calls for it. AM and FM stereo use matrices to get a stereo signal into mid/side, so the mid, which is really just the left and right channels added together, can be used for mono compatibility. The derived side channel in this case, L-R is placed on a subcarrier then recombined with L+R in the receiver to get the stereo channels back. A stereo receiver that goes into mono mode is just muting the side channel so it doesn't get mixed into the matrix. As for an AM stereo transmitter, it's more likely to have a direct mid/side input so that special mid/side processing can be used ahead of time; that's more suitable for AM. FM is more traditional, processed in the left and right domain. Here's something I didn't know about file encoding with M/S: ".. Unlike intensity stereo coding, M/S coding is a special case of transform coding, and retains the audio perfectly without introducing artifacts. Lossless codecs such as FLAC or Monkey's Audio use M/S stereo coding because of this characteristic." From: en.wikipedia.org/wiki/Joint_(audio_engineering)Boomer
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