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Reverse Phase Polarity to hear a difference in processing?

Lets say i have two stereo wav files of the exact same song, but one mixed with some mild saturation, one with no saturation. Other than that singular difference, they are mixed the exact same.

If i want to hear just the added saturation (delta in some plugins) could i just line both of them up in my daw and reverse the polarity on one of the tracks?

Comments

  • @shinyisshiny said:
    Lets say i have two stereo wav files of the exact same song, but one mixed with some mild saturation, one with no saturation. Other than that singular difference, they are mixed the exact same.

    If i want to hear just the added saturation (delta in some plugins) could i just line both of them up in my daw and reverse the polarity on one of the tracks?

    First point is I don’t believe this will produce anything which is of use to listen to! The “extra” saturation is nonsense with the original sound removed…

    Delay and phase change is also likely to mean the nulling is not so complete, but the key point is above… what will the listening tell you?

  • @MadGav said:

    @shinyisshiny said:
    Lets say i have two stereo wav files of the exact same song, but one mixed with some mild saturation, one with no saturation. Other than that singular difference, they are mixed the exact same.

    If i want to hear just the added saturation (delta in some plugins) could i just line both of them up in my daw and reverse the polarity on one of the tracks?

    First point is I don’t believe this will produce anything which is of use to listen to! The “extra” saturation is nonsense with the original sound removed…

    Delay and phase change is also likely to mean the nulling is not so complete, but the key point is above… what will the listening tell you?

    what is happening to my audio when i use a particular plugin, what its adding.

    Whats the best way to null test? i feel like if i line the two wavs up exactly, there woulnt be any delay?

  • edited October 2023

    Hi @shinyisshiny

    I've done this in AUM before thinking I'd just hear the added 'bits' by having two file players, one with inverted phase, bussed together - yes you hear nothing, great so far. So I add an effect expecting to just hear the difference. Mmmm depending on the effect and the phase changes that effect makes sometimes you get what sounds like almost the whole audio back and sometimes just bits of the added effect. It was great learning about what phase changes effects make and not what I had originally expected - try it!

  • @danimal said:
    ... So I add an effect expecting to just hear the difference. Mmmm depending on the effect and the phase changes that effect makes sometimes you get what sounds like almost the whole audio back and sometimes just bits of the added effect. It was great learning about what phase changes effects make and not what I had originally expected - try it!

    You just learned about the influence of a „moving buffer“ ;)
    It‘s impossible to nullify 2 signals that way on IOS or MacOS, at least I never succeeded in hundreds of attempts before I gave up. o:)
    (btw that thing is not called „phase“ but simply „delay“, it‘s time only based and not frequency dependent, which phase is)

  • @shinyisshiny said:

    @MadGav said:

    @shinyisshiny said:
    Lets say i have two stereo wav files of the exact same song, but one mixed with some mild saturation, one with no saturation. Other than that singular difference, they are mixed the exact same.

    If i want to hear just the added saturation (delta in some plugins) could i just line both of them up in my daw and reverse the polarity on one of the tracks?

    First point is I don’t believe this will produce anything which is of use to listen to! The “extra” saturation is nonsense with the original sound removed…

    Delay and phase change is also likely to mean the nulling is not so complete, but the key point is above… what will the listening tell you?

    what is happening to my audio when i use a particular plugin, what its adding.

    Whats the best way to null test? i feel like if i line the two wavs up exactly, there woulnt be any delay?

    If the plugin is linear phase, and latency compensation is correctly working, there isn't much else to it on a theoretical level.
    Have seen it working in some DAW's twenty years ago :)

    Though things can get hairy if both instances have processing of any kind beyond the one effect that's being examined, even if the extra ones are set up with the same params, or indeed were cloned together with the entire track. So one track has to be a truly dry one, or things will be up to chance.

    And yes, phase misalignment is a real issue. It rules out accurate "null testing" methods for many effects.
    That's why some dry/wet controls are a bit dodgy, and worse yet, may have sampling rate dependent cancellation/amplification profiles. Probably nothing too serious when used as part of creative effects, though a good audio engineer needs to be aware of the phenomenon.

  • @Telefunky oooo stop it :D you have just taken me right back to Signals and Systems theory at Uni - these were the lectures I learned how to play pool and drink vodka during - thank you for the memory :#

  • edited October 2023

    Inverting the phase of one and adding both waves will result in their difference (which will probably just be some low rumble and noise).
    But that is with mono. With stereo you have to use some software that handles it by channel, or do it channel by channel yourself.
    And of course it will only work if the two waves are phase aligned to begin with. Even 1-sample offset may corrupt results.

    Your question brings me flashbacks of trying to do DIY acappelas 15 years ago

  • Now all you kids have to do is push a button

  • edited October 2023

    @danimal no magic wand or studies required, it‘s as simple as @quantovox wrote:

    ... there isn't much else to it on a theoretical level.
    Have seen it working in some DAW's twenty years ago :)

    Note the emphasis on 20 years ago, exactly my own experience and I‘ve done it countless times, even with analog gear on outboard paths to precisely time-align DAW channels.
    Buffers were fixed back then and sometimes even delay (in samples) was published for certain operations, so you could add time of sections to get the precise amount for the whole chain.

    Methods have changes since then (and I didn‘t bother with the details), so my description may be inaccurate. Afaik there are „safety buffers“ in addition to the regular buffer size published in an audio system‘s specs.
    It seems the respective app controls the use and output results are precise.
    (as you can easily detect by ear)
    But for a null test now there‘s no more point at which to grab the data to compare, because it (kind of) drifts forward and backward.
    It was a puzzling experience when I noticed it the 1st time: how in hell can the mix be perfectly aligned, when individual signals are moving ???

    Anyway, it‘s not very useful for the original question (judging a signal and it‘s processing parts individually).
    A 100% wet response of a high quality reverb may sound like shite, but mixed with the signal it can be just gorgeous o:)

  • thanks for the input all. Curious does anyone know how some plugins offer "delta" monitoring??

  • It would probably be more useful to use a spectrum analyzer that can show the difference between two spectra, as that prevents any phase issues and provides an actual visual representation of what gets added or removed.

  • @shinyisshiny said:
    Lets say i have two stereo wav files of the exact same song, but one mixed with some mild saturation, one with no saturation. Other than that singular difference, they are mixed the exact same.

    If i want to hear just the added saturation (delta in some plugins) could i just line both of them up in my daw and reverse the polarity on one of the tracks?

    SumFX allows to invert polarity, so you can theoretically cancel a signal S with its inverted image S’.
    https://apps.apple.com/fr/app/sumfx/id6450494474

    Practically, I tried but cannot manage to exactly cancel the signal (we can still hear a bit of the original S signal).
    That’s weird because both S and S’ were inserted in 2 exact instances of the plug-in, so latency should also be compensated.

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