|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
63.246.183.22
In Reply to: RE: Its called " Listening with correct ABSOLUTE PHASE " posted by Palustris on November 14, 2015 at 09:31:20
Many of the processes used along the way aren't 0° or 180°, they're somewhere in-between. In addition, it's almost certain that processing equipment will impart a phase shift across the audible spectrum. The latter renders absolute phase impossible, except over an ill-defined band of frequencies. Then there's the fact that various sources may not be miked in the same way or at the same distance. In the end, if you really feel the need for this, you'll have to play the instrument yourself. :)
--------------------------
Buy Chinese. Bury freedom.
Follow Ups:
"Many of the processes used along the way aren't 0° or 180°, they're somewhere in-between. In addition, it's almost certain that processing equipment will impart a phase shift across the audible spectrum. The latter renders absolute phase impossible, except over an ill-defined band of frequencies. Then there's the fact that various sources may not be miked in the same way or at the same distance. In the end, if you really feel the need for this, you'll have to play the instrument yourself. :)"
TK: I am sure you are right, and for these various reasons it is in practice unlikely that the effects of absolute polarity would be discernible, even if they might in principle be in "ideal" circumstances.
I have wondered, though, as to whether there might be a possible, related, effect that might be more relevant; an effect that is more or less specific to SET amplifiers: The distinguishing feature of an SET amplifier is that it can have a very large amount of second-harmonic distortion, and this means that it is an asymmetric distortion, which implies the positive-going part of the waveform is distorted differently from the negative-going part. For example, the positive half of the waveform may be "compressed" in comparison to the negative part.
The loudspeaker is also, typically, an item that introduces a large amount of distortion, and this also may well have a high proportion of second-harmonic distortion, meaning again an asymmetry between how it distorts the positive part of the waveform and the negative part. (For example, a different behaviour when the cone moves outwards from the magnet, as opposed to when it is drawn into the magnet.)
Now, is we put these two components (SET amplifier and loudspeaker) together, then depending on the polarity of the connection between them, the asymmetry of the distortion by the amplifier may either be reinforced by the asymmetry of the speaker distortion, or it may be partially compensated by it.
Thus, one could imagine that there might indeed be an audible difference between the two possible polarities of the connection of the speaker to the amplifier. Since the distortions of both speaker and SET amplifier are quite large, the effect might perhaps be quite noticeable.
This sensitivity to the absolute polarity would, of course, have nothing whatever to do with the absolute polarity of the source signal from the CD player. In practice, when people claim to hear the effects of absolute polarity, I presume they are doing the switching of polarity in the amplifier to speaker connections, since there would be no convenient way, typically, to switch the polarity of the signal at the input to the amplifier.
Also, the effect I am talking about would be one that is almost exclusively confined to the case of SET amplifiers, because they are almost unique in generating dominant second-harmonic, and large, asymmetric, distortion.
I wonder if anyone has checked for this rather distinctive phenomenon?
Chris
The idea of absolute phase is that ideally when sound pressure depresses the microphone diaphragm, we want the speaker to push the cone outwards. Right? It doesn't matter how many phase reversals occur during the mastering and distribution chain as long as the phase is ultimately correct at the speaker.Now consider that sound is mostly sine waves due to our atmospheric pressure, but square waves would behave the same. So if the audio signal is out of phase by 180 degrees, it will just be half time delayed by the frequency period at that moment. Note that the sound doesn't simply depress the microphone diaphram, it vibrates it. Same goes for the speaker cone.
And considering that everything else, i.e the whole orchestra/band will also be delayed by the same relative amount, how can this be audible? Consider this analogy, the recording was made lets say in 1965. How much time phase shift has occurred by 2015 when we play it. It's irrelevant!
Of course if different microphones are out of phase during the recording process, that cannot be corrected on the playback side - at least not with a simple DPDT switch.
Edits: 11/20/15
"And considering that everything else, i.e the whole orchestra/band will also be delayed by the same relative amount, how can this be audible?"
Well, I think a claim would be that the waveforms of certain musical instruments are actually quite asymmetrical as between the positive half of the wave and the negative half. This would mean that turning the waveform upside down and shifting by half a period would not give back the same thing. I found a couple of examples on the webpage below; for instance, the flute seemingly gives quite an asymmetry of this kind.
Now, imagine listening to such a recording on a loudspeaker that itself has an asymmetric response to positive vs. negative voice coil current. Perhaps, for example, the inward cone displacement for a given current might be larger in magnitude than the outward displacement for the same but sign-reversed current, because the coil is drawn into a stronger magnetic field when the cone moves inwards. Presumably in principle the sound of the flute that one then hears coming from the loudspeaker could be different depending on whether the upper half of waveform of the flute is pushing the cone outwards, or instead is pulling it inwards.
So I suppose whenever there are (at least) two elements along the chain of the sound reproduction process that each have an asymmetry between positive and negative, then one has the possibility that switching the polarity somewhere along the chain between those two elements will produce a different sound as perceived by the ultimate element in the chain (the listener in his living room).
Elements in the chain that might have a positive/negative asymmetry include the amplifier (especially if an SET, which has high second-harmonic (asymmetric) distortion), the loudspeaker, and, I suppose, the ears of the listener. And then another element in the chain that might have a positive/negative asymmetry is the musical instrument, or voice, of the performer in the recording studio. We would not call this asymmetry a distortion, but, rather, just a characterisation of what that particular instrument or voice "actually" sounds like.
Anyway, I suppose that whenever the recording involves instruments or voices with a positive/negative asymmetry, and if there is also another asymnmetrically-distorting link in the chain, then one can in principle end up with different perceived sounds in the living room, depending on whether or not one makes a polarity reversal of the signal (further back along the chain than the asymmetric distorter).
I would suppose that loudspeakers, and SET amplifiers, are the prime candidates for introducing such asymmetric distortions. And of course, if one has both an asymmetrically-distorting loudspeaker and an asymmetrically-distorting amplifier, then the polarity of the connection from the amplifier to the loudspeaker will also affect the sound, quite independently of any issues associated with the polarity of the signal from the CD player.
I'm not sure whether any of these considerations necessarily imply that it is better to keep the polarity between microphone and loudspeaker to be the "correct" one. If one polarity sounds different from the other, then human nature being what it is, one will almost certainly decide that one of the options sounds nicer than the other. But whether that necessarily has to be the one that has the "correct" polarity is perhaps not so obvious.
As to which, if any, of these effects can be expected to be sufficiently pronounced to be audible, I don't really know. My feeling is that a distorting loudspeaker coupled to a distorting SET would probably give quite a noticeable effect (independent of any polarity reversal in the signal from CD player).
I was a little surprised to see how much asymmetry there can apparently be in the waveform of a musical instrument like a flute, and so maybe I would have to revise my previous estimate that one would be very unlikely to be able to hear the effect of switching the polarity of the audio signal from the CD player. But on the other hand, if one were only able to hear the effect of the polarity reversal because one was listening through highly-distorting speakers, or through a highly-distorting amplifier, then would that really "count" as an honest example where the absolute signal polarity needs to be preserved? (Maybe the wrong-polarity version might actually sound nicer, after all!)
I wonder how much positive/negative asymmetry there is in the response of the human ears? One would not, I suppose, call that a distortion, but rather, just "the way we hear things." So if one directly listened to a flute, and one could hear the difference between that and an "anti-flute" whose waveform was upside down, then I suppose one could consider it important to arrange for the audio system to reproduce the flute as a flute and not an anti-flute.
All in all, I think it is an interesting topic.
Chris
If you are using field coil speakers .. try switching the polarity on the power supply side.. that way you don't flip the polarity on the spk binding post, you simply switch the polarity on the field coils.. so the SET connections remains the same all the time..
Gotta try this..... using 8" FC's presently !
Willie
Flipping the polarity of a field coil has the same effect as flipping the speaker wires so I don't see that as a viable option. The generation of the even harmonics is based on the direction of the cone movement and the relationship to the existing even order distortions within the driving system.
dave
I agree! switching speaker terminals with SE amps is not a valid way to invert polarity. When I do it, I often hear a difference but when I use a method that inverts in the digital domain I do not.
dave
"I agree! switching speaker terminals with SE amps is not a valid way to invert polarity. When I do it, I often hear a difference but when I use a method that inverts in the digital domain I do not."
That's very interesting, that you can confirm that! I did, in the meantime, try some googling on the topic, and I found some similar kinds of suggestions out there; that it could be something to do with the distortion profiles of the SE amplifier and the loudspeaker acting either "in parallel" or "in anti-parallel."
I wonder, then, what evidence there is for audible differences that are actually due to polarity reversal of the audio signal from the signal source? Have you yourself, I wonder, ever heard differences when inverting the signal, as opposed to the speaker leads? It seems to me it would have to be an incredibly subtle effect, and while I wouldn't go so far as to say that it must certainly be inaudible, I would be very surprised if it could be reliably detected with normal kinds of music and listening environments.
I can imagine that most people who try the absolute polarity reversal experiments do it by reversing the polarities at the speaker terminals, and for an SET amplifier I could easily believe that would have audible effects. And indeed, one might very well want to make the polarity choice that sounds better (whatever that means!). But that would be unrelated to any absolute polarity issues in the individual recordings. (Though it might be that for other reasons, the sonic signature with one choice of speaker polarities might sound more attractive with some recordings, and the other polarity choice might sound nicer for other recordings.)
Chris
I think when it comes down to it, (most) speakers generate even order distortion and all systems (from the source material to the speaker) also have some form of even order distortion. While you may have individual parts of a system that do not generate copious amounts of even (pp amps), that doesn't account for the stage to stage relationship of the existing even order. Even order summing in phase creates more even, even order summing out of phase creates higher order odd.
dave
Absolute phase isn't a new concept, and I remember that it was investigated by a few reputable groups in the mid-'80s. The double-blind results were indistinguishable to listeners who were generally regarded as being "audio-aware." :) That was with solid state gear however, not tubes, so I can't respond to potential results using an asymmetrical amplifier. On the other hand, distortion in the SETs I build is very low, so much so that I don't consider their even-order contribution to be sufficient to produce an audible sonic signature.Incidentally, even-order distortion is not confined to positive-negative asymmetry. A square wave can generate huge amounts of even-order energy and still be completely symmetrical in this way. It only need have a duty cycle other than 50%. I have personally witnessed this effect using lab-grade spectrum analyzers and variable duty cycles, and it can be simulated using the FFT function in SPICE programs. The point I'm making is that if absolute phase were audible (and I believe it's not), an asymmetrical amplifier probably isn't required in order to hear it.
--------------------------
Buy Chinese. Bury freedom.
Edits: 11/15/15 11/15/15
"The point I'm making is that if absolute phase were audible (and I believe it's not), an asymmetrical amplifier probably isn't required in order to hear it."I agree with you; I doubt very much that absolute phase, in the sense normally understood, is audible. If it were audible, it would presumably only be in subtle effects at the start of percussive sounds, and suchlike, and it seems very hard to believe that one would ordinarily be able to notice these. And if a claimed audibility could not be confirmed in double-blind tests, it would indeed be reasonable to conclude that it was imagined rather than real.
It certainly would not seem to be at all consistent with the kind of "night and day" differences reported by the OP: "As for brightness, with the polarity switched the Sophias are in fact rather lush and dark."
I guess I was trying to be charitable, and wondering if there was any conceivable phenomenon that could account for what was reported. I still feel that if there were a couple of percent of asymmetric distortion in the amplifier, and another couple of percent of asymmetric distortion in the loudspeaker, then it is not implausible that the audible sound could be significantly different depending on whether the polarity of the loudspeaker's distortion was, so to speak, parallel or anti-parallel with that of the amplifier. The effect, if it were significant, could occur even with a pure sinewave as a signal source; it would not in any way depend on the ordinarily understood notion of the absolute phase of the audio signal in the CD recording, which I would consider to be essentially irrelevant in any case. And it would be a continuous (in time) effect, much more in line, perhaps, with what the OP reported.
I know nothing about the distortion levels in the OP's amplifiers and speakers, so I don't know whether such effects could be significant or not. But I would certainly be willing to bet that if instead the polarity of the audio signal going into the amplifier (both amplifiers, in the case of stereo) were reversed, there would be no audible difference. (At least, no difference that could be confirmed in double-blind tests.)
By the way, although it may not be pertinent to the present discussion, I would call a rectangular wave, with duty cycle not equal to 50%, asymmetric in the sense I meant. That is to say, the sign-inverted signal is not equal to a time-translated version of the original signal.
Chris
Edits: 11/15/15 11/15/15
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: