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Phase invertion

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  • #31
    Originally posted by yeecn View Post
    More interesting stuff from

    Hair cells act as a half-wave rectifier. We are unaware of the (negative) half of the waveform.
    Quite mind-boggling. Does that means that we will only ever get to hear half the music (so to speak)?

    What is even more mind-boggling is that the way the nerve cells fire at positive zero crossing of the waveform - that is a quantum even that is similar to taking a digital sample. Human hearing is digital in nature!

    I am still trying to digest the many intriguing facts in the article. Below is point that caught my attention a few moments ago:

    Human hearing adapts to errors in spectrum and timbre over a period of 10 to 20 minutes.
    - Even an old fashioned phonograph sounds pretty good once you get used to it!
    - And many of the monitoring loudspeakers in common use are severely colored.
    - The people who use them say they sound fine.


    • #32
      Polarity of audio signal through the audio chain

      I was first introduced to the issue of polarity inversion when I bought a YBA 2 Delta preamp that inverts absolute polarity. They recommend reversing the speaker leads to counter this; stating that incorrect polarity results in a "harshness" in the frequency extremes and a softening of transients. Dutifully, I did as the manufacturer recommended, but I wanted to see for myself what change this would make. I decided on 3 different tracks to listen to for comparison and switched the leads as quickly as possible. Something had changed, but I wasn't sure it had improved. What I heard did not agree with what the manufacturer suggested (harshness in highs / lows, and softening of transients), but I figured it was best to preserve absolute polarity so I kept the speaker terminals reversed.

      Some time later, I came to learn that my DAC, Bel Canto DAC 3, also inverts absolute polarity. Therefore, by switching the speaker leads, I had inverted absolute polarity. With this in mind I changed the leads back, and researched all of the components in my system. The preamp and DAC were the only inverting components so this put me in a good place for some A/B comparisons. I could play a track through my (non-inverting CD player) and the preamp would invert it. If I played the same track through the DAC, it would be twice inverted and therefore in correct polarity at the speakers. Of course, with this setup, there were also differences in the D to A sections of the 2 components and matching levels exactly proved difficult. No hard and fast conclusions emerged; I would try to listen more for the leading edge of a particular transient rather than the overall presentation or differences in tonality.

      After an hour or so of this, it all really started sounding the same to me. One theory after the next would collapse before my ears. I read up on the phenomenon and learned many of the same things mentioned here about polarity of the recording and even individual instruments. There are people who can reliably differentiate between absolute and inverted polarity. In fact I found a blind test online where you can determine whether you are truly sensitive; http.// I learned that I am not sensitive to absolute polarity.

      I don't know whether this effects my findings or not, it is worthy of mentioning in any discussion of absolute polarity with regard to Harbeth loudspeakers. Harbeth wires their tweeters in reverse electrical polarity to help with {correct acoustic polarity and} time delay. I discovered this on my own when I opened the pair to have a look inside. I contacted the company about this and they told me that this is how my M-30's should be wired. Actually, I'm not sure whether this is true for just my speakers or the others in the lineup as well. This fact helped me to lay the issue to rest once and for all.

      {Moderator's comment: Do you know the polarity of the microphones, mixing desk, CD mastering at the production end of the music chain? Obviously not. So it's not possible to be 100% sure of the absolute polarity of any music signal arriving at home. You have found out that even through the home audio chain, phase can be flipped. Please don't be anxious about absolute phase. For music, absolute phase is unlikely to be detectable.}


      • #33
        Phase switch - a waste of a switch?

        In the past, I have had several products which allow absolute phase to be reversed at the touch of a button on the remote. With everything set up just so, a small 'difference' could sometimes be discerned when switching back and forth.

        I would stress the 'difference' and never an improvement one way or the other. To my mind, such a facility is a waste of a switch.


        • #34
          Fooling oneself for fun and phase...

          Originally posted by hifi_dave View Post
          With everything set up just so, a small 'difference' could sometimes be discerned when switching back and forth.
          There have been many occasions when I've {in my capacity as a professional sound engineer} operated a switch and thought, at that instant, "Wow - I never expected THAT to happen" (whatever THAT happened to be). Trying it again a few times, I realised that I had reacted to the switching operation itself, not any real difference that exists on either side.

          Switches cause transient disturbances, no matter how good they are. For a laugh I once altered the absolute phase of some music and edited at a zero crossing point between the original and phase-inverted samples.

          Suffice it to say that the edit itself was inaudible and nothing felt any different on either side.

          BUT read this.


          • #35
            The phase demonstration - and best wishes

            Originally posted by Pluto View Post
            T...For a laugh I once altered the absolute phase of some music and edited at a zero crossing point between the original and phase-inverted samples. Suffice it to say that the edit itself was inaudible and nothing felt any different on either side...
            Now that is such a brilliantly simple and effective way of laying the phase issue to rest that I'm kicking myself that I didn't think of it! I wonder if it is clear to the membership just how elegant a demonstration of the utter non-importance of 'phase' is?

            I would very much like to encourage you to make that demonstration sound clip, and to accompany it with a screen snap of two of how you selected the cut point (the zero crossing point). However, I'm aware that in the next few days you will be hospitalised and on behalf of the entire membership wish you home and fit as soon as possible. I for one greatly respect and enjoy your contributions here. Maybe this can be your recuperative contribution if you feel up to it?

            All the best
            Alan A. Shaw
            Designer, owner
            Harbeth Audio UK


            • #36
              My phase demonstration ....

              Originally posted by A.S. View Post
              ...Maybe this can be your recuperative contribution if you feel up to it?
              With great pleasure, all being well.

              Many thanks for your good wishes - I'll keep you posted!



              • #37
                Significance of absolute phase - an audio demonstration

                NOTE: Ignore MP3 player section (marked). Use only Flash player.

                Here are two short excerpts from the magical 1958 Britten recording of Peter Grimes, recently discussed here. Each contains a switch in absolute phase about half way through. Just to be entirely unambiguous about what we mean here, absolute phase is when both L & R sides of the stereo signal simultaneously change phase, not to create an obvious and disastrous out of phase condition but rather, a far more tenuous state that some claim to be audible and therefore insist must be maintained correctly despite a number of unknowns in the recording chain.

                See if you can detect the moment of switch in either of the attached clips. Why two clips? It's due to the nature of the material. This recording exhibits truly fabulous use of stereophony; nicely wide and ambient. This implies that the recording contains a lot of legitimate out-of-phase content. The extra "information" required to create stereo (compared to mono) is always out of phase; if you find this hard to accept, trust me for now and we'll go into it later.

                I'm making a presumption that the more out of phase content that is contained within a recording, the less obvious any kind of phase reversal (simultaneously to both channels) will be. To prove this point, you could play "The Storm" Sea Interlude entirely with one of the L & R channels out of phase with the other, while it would sound odd, it's unlikely to sound terrible. Whereas a simple central mono image of a single male voice would, if played back with one of the channels out of phase, sound truly nauseous and cancel out entirely if the L & R signals are combined electrically to produce a single (mono) signal.

                "The Storm" is a magnificent piece of really wide stereo content. "You Sailed Your Boat" has far more modest stereophonic credentials, so I've included both clips to avoid any suggestion that the issue of absolute phase is, in any way, programme dependent.

                Have a listen to the clips and see if you can tell where I've placed the transition from the entire recording in normal phase to an instantaneous switch to the entire recording out of phase. The boss knows where, so he's the ref!

                Grimes Phase Test #1

                Grimes Phase Test #2

                Can you hear where the phase of the entire L and R signal flips by 180 degrees?


                • #38
                  How about phase in a sine wave?

                  So what about inverting a portion of a continuous sine tone? Surely if 'absolute phase' is detectable by the human ear, we should be able to hear a change.

                  Because of the way I've edited this sample (I can't edit exactly on the sample point) there is a tiny glitch where I reversed the phase. With more care and a higher sampling rate, I could make the transition inaudible. The little glitch aside, can you hear that for about half of this clip the sound wave from your speaker is in effect pushing air towards your ear (positive phase) and for the other part sucking it backwards towards the speaker (crude analogy). Obviously not.

                  Alan A. Shaw
                  Designer, owner
                  Harbeth Audio UK


                  • #39
                    My feedback on phase swap

                    Re: GPT2
                    Did you change the phase somewhere where the line "You mean you threw the fish overboard" starts, around 0.36s?

                    Re:Sine wave.
                    Just after the edit click I feel the tones lose a little intense but quickly it becomes indistinguishable.



                    • #40
                      Improving the experiment

                      Re: Sine wave clip

                      I think changing the absolute phase in between the clip may creates changes to the air pressure which our ears may able to detect at the spot where change took place because the movement of the cones from pushing the air forward and then changing the motion to suck may result in some changes in the air pressure momentarily at the that particular point of switch over.

                      Maybe a better way to do this experiment is to have the two or more clips of sine wave recorded randomly in different phase.



                      • #41
                        Hi there

                        The reason for phase button is to eliminate some audiophiles suspicions about correct phase of the disc. And another issue is that most of pirate records (Bulgarian for example) seems to be recorded in inverse phase (this could be a reason for a poor audio quality)... this could be a reason for good or bad records…

                        1. plug phase (IEC) – some brand preffer to inverse phase in order to work better with their cable or with same brand components.
                        2. microphone phase – in order to obtain the accurate reproduction of sound probably the best sound engineers know this litlle secret of correct microphone phase checking.
                        3. speaker phase – here is no doubt that factory specifications for + and – must be respected…

                        So this phase standard seems to be a troian horse against audiophile. If u are a dealer u can switch phase of IEC in order to make some electronic device sound better or worse depend of your personal sale interest.
                        If u are a company who produce a variety of products from media centers to speakers, u have a better control of this … u can make a beter compatibility between electronix.
                        If u make just speakers u have also two options : u can ignore the phenomen or not. 

                        In other way... I still preffer easy ways to make things works.

                        Best regards


                        • #42
                          Simple phase checker

                          Speaker polarity check test: