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Thread: Mono Recordings Converted to Stereo

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    Senior Member adriesba's Avatar
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    Default Mono Recordings Converted to Stereo

    I'm just curious, what exactly is done to recordings when they are converted from mono to stereo, like the recordings at Pristine Classical?

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    Senior Member joen_cph's Avatar
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    I don't know about recent attempts, supposedly one can do better things digitally. Interesting. But originally, on LPs several decades ago, the results were mostly poor, the mono version usually being preferable ...
    Last edited by joen_cph; Nov-25-2020 at 00:13.

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    Senior Member Becca's Avatar
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    You can't convert mono to stereo because that would require using information that doesn't exist in the recording, all you can do is fake out the ear to think that there is some sense of spatialness [sic!]. While i wouldn't be surprised that there are additional tricks possible with computer processing, typical methods including adding artificial resonance or changing the frequency curve for the left and right channels (higher pitched violins usually being on the left.)

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    Senior Member NoCoPilot's Avatar
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    In the early days of stereo all kinds of tricks were tried to update mono recordings. In rough order of sophistication:
    • the mono signal was played into a room and miced stereophonically. This had the unfortunate effect of making everything sound pretty distant
    • stereo reverb was electronically added to the mono signal. This could keep the primary signal from sounding as distant, but it usually ended up pretty echoey
    • equalizers were set up to divide up the signal, in however many bands the engineer had available. The low end was usually left mostly mono, with maybe a bit of echo added. The higher frequencies were panned and/or reverbed, different settings for different frequencies. If the engineer was good, he could use the equalizer to try to isolate particular instruments, and treat them individually as appropriate for that instrument.
    • with the onset of digital signal processing (DSP) it became possible to DYNAMICALLY follow particular instruments and treat them separately with different panning and reverb, changing as the instruments came & went or went up & down in pitch. Some of these "pitch-following paradigms" got very good.

    However, none of these techniques would ever fool a close listen, especially not on headphones. At least, I don't THINK they would (I guess I wouldn't know, would I?)

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    Senior Member NoCoPilot's Avatar
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    Incidentally, the VAST MAJORITY of contemporary recordings are still "multi-channel mono," where instruments and singers are miced monaurally and then mixed across a stereo field. It is very rare for instruments, except maybe acoustic grand pianos, to be miced stereophonically.

    The exceptions are ensemble recordings where everyone's in the same room, sharing the same acoustic space. This is most often done for chamber groups and orchestras and occasionally jazz ensembles. The musicians and engineers hate recording like this, because without sonic isolation, mistakes can't be pulled out and re-recorded. It's a true measure of the professionalism of an ensemble to be able to record together without the occasional flub.

    Of course some engineers just leave 'em in.....
    Last edited by NoCoPilot; Nov-25-2020 at 02:56.

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    Senior Member Kiki's Avatar
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    Quote Originally Posted by Becca View Post
    You can't convert mono to stereo because that would require using information that doesn't exist in the recording, all you can do is fake out the ear to think that there is some sense of spatialness [sic!]. While i wouldn't be surprised that there are additional tricks possible with computer processing, typical methods including adding artificial resonance or changing the frequency curve for the left and right channels (higher pitched violins usually being on the left.)
    I absolutely agree, what does not exist cannot be re-created.

    Altus has released a CD of Mravinsky's 1963 live Sibelius 3 containing both the original mono mix and a quasi-stereo mix. Altus said they manipulated the frequencies and the soundstage. I can tell there is a difference between the 2 channels but the difference is minute, so for example the violins don't noticeably appear on the left. However, this minute difference is sufficient to make the recording sound more "open", which is quite amazing, but it definitely does not sound like real stereo. What's not there is not there and cannot be re-created.

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    Quote Originally Posted by Becca View Post
    You can't convert stereo because that would require using information that doesn't exist in the recording, all you can do is fake out the ear to think that there is some sense of spatialness [sic!]. While i wouldn't be surprised that there are additional tricks possible with computer processing, typical methods including adding artificial resonance or changing the frequency curve for the left and right channels (higher pitched violins usually being on the left.)
    You can have both. If two mikes are used, and one is back/front stereo and the other is a condenser mike pointed to the front, a stereo signal can be manipulated from full stereo to full mono, or anything in between, by using a "matrix" mixer. This was used when mono mixes were needed for broadcast.

    M/S technique: mid/side stereophony


    This coincident technique employs a bidirectional microphone facing sideways and another microphone at an angle of 90°, facing the sound source. The second microphone is generally a variety of cardioid, although Alan Blumlein described the usage of an omnidirectional transducer in his original patent.
    The left and right channels are produced through a simple matrix: Left = Mid + Side; Right = Mid − Side (the polarity-reversed side signal). This configuration produces a completely mono-compatible signal and, if the Mid and Side signals are recorded (rather than the matrixed Left and Right), the stereo width can be manipulated after the recording has taken place. This makes it especially useful for film-based projects.
    Last edited by millionrainbows; Nov-27-2020 at 15:40.

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    Quote Originally Posted by Kiki View Post
    I absolutely agree, what does not exist cannot be re-created.

    Altus has released a CD of Mravinsky's 1963 live Sibelius 3 containing both the original mono mix and a quasi-stereo mix. Altus said they manipulated the frequencies and the soundstage. I can tell there is a difference between the 2 channels but the difference is minute, so for example the violins don't noticeably appear on the left. However, this minute difference is sufficient to make the recording sound more "open", which is quite amazing, but it definitely does not sound like real stereo. What's not there is not there and cannot be re-created.
    I know of another recording like that: John Cage 25-Year Retrospective (2-CD Wergo). It's labelled as mono, but upon close listening through headphones is revealed to be stereo, although nearly coincident.

    Last edited by millionrainbows; Nov-27-2020 at 15:48.

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    Senior Member pianozach's Avatar
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    I'm a proper sound engineer, but the technology today is astonishing.

    I record excellent quality demos, and there's a lot that can be done . . . I simply don't record any midi. I've recorded acoustic guitar both line-in and by microphone simultaneously.

    My virtual instruments, especially keyboard instruments are pointedly stereo. I can pan voices one way or the other while assigning reverb to the opposite channel. I'll duplicate a track, mix them to different sides with completely different EQ, reverbs or other sound alterations. With a push of a button I can spread out a mono track digitally.

    And I'm an amateur.

    Here's a pro company that does Mono to Stereo conversion. I'll bet they get pretty damned convincing results.

    http://www.alango.com/technologies-mono2stereo.php

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    Senior Member NoCoPilot's Avatar
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    Quote Originally Posted by Alango
    Alango mono-to-stereo conversion technology works by:

    1. Dividing the original mono sound into frequency regions (frequency bands);
    2. Introducing signal delays between corresponding frequency bands in the right and left channels simulating the time of arrival differences;
    3. Introducing amplitude difference between signals in frequency bands corresponding to the left and right channels and thus simulating the head acoustic “shadowing” effect. Generally, we can anticipate sounds arriving earlier as being stronger.
    Yep, that's a combination of the 1st and 3rd techniques I mentioned above in post #4. The twist is they're apparently using an "artificial head" (Kunstkopf) system to simulate binaural sound when re-recording the monaural signal. Quite a few recordings marketed as "binaural" have been mono recordings processed this way.

    True binaural sound of course is a different kettle of fish altogether.
    Last edited by NoCoPilot; Dec-16-2020 at 00:26.

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    'Electronically Enhanced for Stereo' usually means it sounds like it was recorded in an echo chamber

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    Senior Member pianozach's Avatar
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    Todd Rundgren
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    ". . . or mono reprocessed for stereo . . . "

    Last edited by pianozach; Mar-03-2021 at 05:01.

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    Most of my listening is stereo converted to mono. Works a lot better than mono converted to stereo, especially the original Dylan album where I recall the stereo version had his guitar in one speaker and his voice in the other.

    I use a single earbud that combines both channels to a mono signal. Sure, stereo sounds better, but it would limit my listening time severely. At least this way I can listen a lot while still having an ear open to participate in what is going on around me.
    Last edited by SixFootScowl; Mar-03-2021 at 05:16.
    “The media’s the most powerful entity on Earth. They have the power to make the innocent look guilty and to make the guilty innocent, and that’s power. Because they control the mind of the masses.”
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    Senior Member NoCoPilot's Avatar
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    Quote Originally Posted by SixFootScowl View Post
    I use a single earbud that combines both channels to a mono signal. Sure, stereo sounds better, but it would limit my listening time severely. At least this way I can listen a lot while still having an ear open to participate in what is going on around me.
    That's what "open-ear headphones" are for; they allow you to still hear outside sounds. A friend of mine was stopped by police one day for driving while wearing headphones. He politely explained to the officer that he was listening to language-learning tapes on open-ear headphones, and had the officer try them on. The officer was able to confirm that he heard the tape, but also heard all the ambient sounds around him.

    He let my friend go on about his business, didn't even write him up a warning.

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    Senior Member SixFootScowl's Avatar
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    Quote Originally Posted by NoCoPilot View Post
    That's what "open-ear headphones" are for; they allow you to still hear outside sounds. A friend of mine was stopped by police one day for driving while wearing headphones. He politely explained to the officer that he was listening to language-learning tapes on open-ear headphones, and had the officer try them on. The officer was able to confirm that he heard the tape, but also heard all the ambient sounds around him.

    He let my friend go on about his business, didn't even write him up a warning.
    Open ear? Is that where the backs are not totally covered? I have one like that and the problem is other people can hear my music. But I don't wear headphones when I am out and about because they are too cumbersome, where the earbud is very compact. Good to know though.

    Your friend probably could hear outside sounds better than a lot of people who just play the car stereo.
    “The media’s the most powerful entity on Earth. They have the power to make the innocent look guilty and to make the guilty innocent, and that’s power. Because they control the mind of the masses.”
    --Malcolm X

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