Sound localisation
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From: And Blah Blah Blah on 1 Feb 2006 14:48 I am doing research into sound localisation for a degree project and how to alter signals to affect their apparent position. I understand how and why time delay and amplitude difference between the ears have an effect as well as spectral changes. However I keep finding references to phase differences being an important cue and I don't understand what a phase difference would be in this context (why is it different from a time delay) and where it would come from. Non of the references offer an explaination that I can understand so I wonder if anyone here can clear the matter up for me. Thanks for any help Richard
From: Rune Allnor on 1 Feb 2006 15:09 And Blah Blah Blah wrote: > I am doing research into sound localisation for a degree project and how > to alter signals to affect their apparent position. I understand how > and why time delay and amplitude difference between the ears have an > effect as well as spectral changes. However I keep finding references > to phase differences being an important cue and I don't understand what > a phase difference would be in this context (why is it different from a > time delay) and where it would come from. Non of the references offer > an explaination that I can understand so I wonder if anyone here can > clear the matter up for me. First, you might want to change the nickname that is displayed in the "name" field, to get more useful responses. Time differences and phased ifferences are basically the same thing. In frequency domain, shifting a signal in time corresponds to changing the phase. For practical purposes, a "phase shift" is a time delay tau that is smaller than the dominant period T, tau < T while a "time delay" is a time shift tau larger than the dominant period T, tau > T. HTH, Rune
From: Jerry Avins on 1 Feb 2006 16:37 Rune Allnor wrote: > And Blah Blah Blah wrote: > >>I am doing research into sound localisation for a degree project and how >>to alter signals to affect their apparent position. I understand how >>and why time delay and amplitude difference between the ears have an >>effect as well as spectral changes. However I keep finding references >>to phase differences being an important cue and I don't understand what >>a phase difference would be in this context (why is it different from a >>time delay) and where it would come from. Non of the references offer >>an explaination that I can understand so I wonder if anyone here can >>clear the matter up for me. > > > First, you might want to change the nickname that is displayed in the > "name" field, to get more useful responses. > > Time differences and phased ifferences are basically the same thing. > In frequency domain, shifting a signal in time corresponds to changing > the phase. For practical purposes, a "phase shift" is a time delay tau > that is smaller than the dominant period T, > > tau < T > > while a "time delay" is a time shift tau larger than the dominant > period T, > > tau > T. If bla bla bla delays an entire signal by a certain time, then each component will be shifted in phase by an amount proportional to its frequency. When a delay of a ms is created, 1KHz is retarded 360 degrees, 100 Hz 36, and DC not at all. (That's why we don't usually talk about the phase of DC. We can take it for granted.) Jerry -- Engineering is the art of making what you want from things you can get. ???????????????????????????????????????????????????????????????????????
From: "The Poster Formally Known As "And Blah Blah Blah"" on 1 Feb 2006 17:59 Jerry Avins wrote: > Rune Allnor wrote: > >> And Blah Blah Blah wrote: >> >>> I am doing research into sound localisation for a degree project and how >>> to alter signals to affect their apparent position. I understand how >>> and why time delay and amplitude difference between the ears have an >>> effect as well as spectral changes. However I keep finding references >>> to phase differences being an important cue and I don't understand what >>> a phase difference would be in this context (why is it different from a >>> time delay) and where it would come from. Non of the references offer >>> an explaination that I can understand so I wonder if anyone here can >>> clear the matter up for me. >> >> >> >> First, you might want to change the nickname that is displayed in the >> "name" field, to get more useful responses. >> >> Time differences and phased ifferences are basically the same thing. >> In frequency domain, shifting a signal in time corresponds to changing >> the phase. For practical purposes, a "phase shift" is a time delay tau >> that is smaller than the dominant period T, >> >> tau < T >> >> while a "time delay" is a time shift tau larger than the dominant >> period T, >> tau > T. > > > If bla bla bla delays an entire signal by a certain time, then each > component will be shifted in phase by an amount proportional to its > frequency. When a delay of a ms is created, 1KHz is retarded 360 > degrees, 100 Hz 36, and DC not at all. (That's why we don't usually talk > about the phase of DC. We can take it for granted.) > > Jerry But am I right in thinking that in the end they are not two seperate phenomonen? Whether the brain sees a shift in the whole signal by given time, or that each frequency has shifted in phase by a different but related angle; it is the same information expressed in a different form? RIchard
From: Jerry Avins on 1 Feb 2006 18:41
The Poster Formally Known As "And Blah Blah Blah" wrote: ... > am I right in thinking that in the end they are not two seperate > phenomonen? Whether the brain sees a shift in the whole signal by given > time, or that each frequency has shifted in phase by a different but > related angle; it is the same information expressed in a different form? Yes, but phase shift proportional to frequency -- so called "linear phase" -- isn't necessarily always the case. There are ways to shift the phase of all frequencies in a broad (but not limitless) band by an arbitrary and equal amount (90 degrees is most common), and so-called all-pass networks can shift phase vs. frequency almost arbitrarily without affecting amplitude response. A good description of what you really want to do or know will deter us (all right; me) from drowning you in unnecessary detail. Sometimes, I feel they "barfing up the book" is the only way I can avoid being misleading. When I know the point, I can stick to it. Jerry -- Engineering is the art of making what you want from things you can get. ??????????????????????????????????????????????????????????????????????? |