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Acoustics of corners
Acoustics of corners
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Old 9th February 2018, 08:10 PM   #151
scottjoplin is offline scottjoplin  Wales
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A rotation of 1800 degrees seems to be excessive, and I don't understand why this was necessary, wouldn't it also likely cause audible smearing of transients?
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Old 9th February 2018, 09:22 PM   #152
AllenB is offline AllenB  Australia
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most part I have not found phase or delay to be meaningful....
Is this because they are in the modal region, or in spite of them being in the modal region and just because of our perception at these frequencies?
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Old 9th February 2018, 09:54 PM   #153
gedlee is offline gedlee  United States
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We're probably thinking/talking from different perspectives I guess.

I don't really see phase rotation and time delay as being the same thing.
FIR, and programs like rePhase, have made it where we can have about any shape phase trace we want, show up at the measuring mic.....all with the same delay.
I don't think that It's simply a difference of perspective, because your second paragraph is incorrect. The "shape of the phase" will dictate the delay. Different shapes have to have different delays. We can have the same magnitude responses with different delays, that's true, but that's not what you are claiming.
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Old 10th February 2018, 02:03 AM   #154
mark100 is offline mark100  United States
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I don't think that It's simply a difference of perspective, because your second paragraph is incorrect. The "shape of the phase" will dictate the delay. Different shapes have to have different delays. We can have the same magnitude responses with different delays, that's true, but that's not what you are claiming.
Yes, I am definitely claiming the shape of the phase does not have to dictate delay.

It doesn't have to with FIR, given enough sample time to alter phase to will.

The necessary sample time shows up only as pure time delay, no different than distance. Phase can be moved all around within a defined sample time, with a constant delay.
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Old 10th February 2018, 02:12 AM   #155
mark100 is offline mark100  United States
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The way I see it a phase shift is a time delay but only for an infinitely long sine wave. It amounts to the same thing but only upto 360 degrees.

I'm not familiar with FIR filters and digital delays, but I'm guessing they can shift phase and delay any shape waveform, ie, it's not frequency dependant and doesn't cause group delay?
you might want to download rePhase and play around with it...it's a hell of a learning tool....or has been for me anyway
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Old 10th February 2018, 02:57 PM   #156
gedlee is offline gedlee  United States
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Yes, I am definitely claiming the shape of the phase does not have to dictate delay.

It doesn't have to with FIR, given enough sample time to alter phase to will.

The necessary sample time shows up only as pure time delay, no different than distance. Phase can be moved all around within a defined sample time, with a constant delay.
I don't know what to say, except that your understanding is incorrect. Phase change with frequency is time delay - period - and this is true in either the digital or analog domains. I'd try and explain the error in your example except that I can't follow it.
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Old 10th February 2018, 06:45 PM   #157
mark100 is offline mark100  United States
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I don't know what to say, except that your understanding is incorrect. Phase change with frequency is time delay - period - and this is true in either the digital or analog domains. I'd try and explain the error in your example except that I can't follow it.
Maybe I'm misusing or misunderstanding definitions....

So,... my understanding is "time delay" means just that, and nothing past that. And that time delay is a constant, and frequency independent.
Examples being things like distance, fixed dsp latency, a digital delay, or FIR filters.

My understanding is "phase change with frequency, or phase rotation over frequency", is a relative relationship of frequencies' phase versus the phase of a given reference frequency at some point in time (usually nyquist freq, with all "time delay" removed).

I can see that "phase rotation" requires that there is a varying time shift vs frequency,
but I think of this time shift more as a "time rotation" vs frequency...without a clear term to describe it. Or without me having found one yet

So I see time delay, and phase rotation, as describing two very different time properties....

Please advise and thank you for hanging in with me!
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Old 10th February 2018, 06:54 PM   #158
TNT is offline TNT  Sweden
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1800 degrees means they're back in phase, so how is that a time delay? They are related of course
If you don't understand the difference between delay and phase, maybe you should avoid commenting and giving advice on these matters.

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Old 10th February 2018, 07:00 PM   #159
scottjoplin is offline scottjoplin  Wales
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So, you are saying there is a difference? Your advice and comments are, as always, very welcome
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Old 10th February 2018, 07:13 PM   #160
gedlee is offline gedlee  United States
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So I see time delay, and phase rotation, as describing two very different time properties....
Consider the standard physics representation of a signal as a complex exponential V(w) = A(w) * exp^(i * w * t) where w is angular frequency and t is time. This describes a vector that rotates around the origin with an amplitude of A and it makes w full rotations every second. At any instance in time there is a "phase" of this vector, but as time progresses this phase continuously advances. This means that phase and time are simply two different ways of describing the exact same thing - progression of time or progression of phase. They are the same thing not different things.

This is easier to see in the analog domain as things get a little foggier in the digital domain.
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