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Author Topic: Dithering and Phase  (Read 1671 times)

reynaud

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Dithering and Phase
« on: January 17, 2006, 09:40:48 AM »

Greetings,

Does Dithering affect phase or does it just reduce dynamic range? I "activated" Waves IDR with no file open and registered phasing issues (my hardware phase meter was bucking and boosting). Is my meter faulty or does dither affect a phase in some way. I would think that the phase meter should be "flat".

many thanks,
Reynaud
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bobkatz

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Re: Dithering and Phase
« Reply #1 on: January 17, 2006, 10:29:05 AM »

reynaud wrote on Tue, 17 January 2006 09:40

Greetings,

Does Dithering affect phase or does it just reduce dynamic range? I "activated" Waves IDR with no file open and registered phasing issues (my hardware phase meter was bucking and boosting). Is my meter faulty or does dither affect a phase in some way. I would think that the phase meter should be "flat".

many thanks,
Reynaud



You're looking at the random, uncorrelated noise floor of the dither. It's SUPPOSED to do that... The meter will show that the dither floor is randomly wandering, but it should average around the center, "uncorrelated".

Also, if your phase meter is jumping wildly with the dither perhaps its time constants are a bit too fast.

Bottom line: Dither does not affect phase. As soon as you add any normal room tone or ambience to the recording, your phase meter should settle down.

BK
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reynaud

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Re: Dithering and Phase
« Reply #2 on: January 17, 2006, 11:23:58 AM »

thank you for the response. I also noticed that i was getting a low level signal at around -118dBFS Left and about -122dBFS Right. Once a tone is present does this level stay constant or reduce slightly?

thanks for clearing things up,
Reynaud
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dcollins

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Re: Dithering and Phase
« Reply #3 on: January 18, 2006, 01:04:55 AM »

reynaud wrote on Tue, 17 January 2006 08:23

thank you for the response. I also noticed that i was getting a low level signal at around -118dBFS Left and about -122dBFS Right. Once a tone is present does this level stay constant or reduce slightly?

thanks for clearing things up,
Reynaud


You don't have phase "issues," you're just metering low-level noise of the dither.

What word-length was the IDR set?

I'm concerned by the -122, as 16 bit dither should be more like -90 peak.  That's more like 24 bit dither.

Dither sets the minimum phase resolution of the system, so in that way it does have a effect......

DC

Ronny

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Re: Dithering and Phase
« Reply #4 on: January 18, 2006, 02:26:00 AM »

dcollins wrote on Wed, 18 January 2006 01:04

reynaud wrote on Tue, 17 January 2006 08:23

thank you for the response. I also noticed that i was getting a low level signal at around -118dBFS Left and about -122dBFS Right. Once a tone is present does this level stay constant or reduce slightly?

thanks for clearing things up,
Reynaud


You don't have phase "issues," you're just metering low-level noise of the dither.

What word-length was the IDR set?

I'm concerned by the -122, as 16 bit dither should be more like -90 peak.  That's more like 24 bit dither.

Dither sets the minimum phase resolution of the system, so in that way it does have a effect......

DC




I've always wondered about that. I read in a manual or two that dithering increases dynamic range by around -10dB. I thought that they meant perceived gain not actual gain measured inside a system, like what Waves says about IDR making the final 16 bit perceived more like 19 bits of resolution. I'm not saying that I agree with them, but I've seen Digicheck show -107dB when inputting a  32 bit dithered to 16 bit signal. Can anyone explain what's happening here?
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dcollins

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Re: Dithering and Phase
« Reply #5 on: January 18, 2006, 02:44:31 AM »

Ronny wrote on Tue, 17 January 2006 23:26


I've always wondered about that. I read in a manual or two that dithering increases dynamic range by around -10dB.



And they would be wrong.

What dither actually does is to make digital systems work just like analog ones.......

This must have been in a book, somewhere, by now.

Quote:


I thought that they meant perceived gain not actual gain measured inside a system, like what Waves says about IDR making the final 16 bit perceived more like 19 bits of resolution.



Although you may either have to stick your head in the speaker, or have a very quiet room, to hear differences at the LSB.

Quote:


I'm not saying that I agree with them, but I've seen Digicheck show -107dB when inputting a  32 bit dithered to 16 bit signal. Can anyone explain what's happening here?



If your meter is right, then the amplitude is wrong.  Do you have it set to 18 bit?

DC


lagerfeldt

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Re: Dithering and Phase
« Reply #6 on: January 18, 2006, 07:59:18 AM »

BTW; don't you find the IDR bothersome? Try the POW-r#3, it's usually a better choice in most cases IMO.

Joe Crawford

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Re: Dithering and Phase
« Reply #7 on: January 18, 2006, 12:27:51 PM »

When it come to a technical understanding of dither a picture is sometimes worth a thousand words.  You can generate a short wav file of only dither (i.e., the type and bit depth you're interested in)and then run an audio analyzer against it such as Right Mark (free at www.audio.rightmark.org).  This will show you both the frequency distribution and signal strength of the dither.  You can also check it out with other analysis tools such as a phase scope, bit meter, etc.

Joe
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Ronny

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Re: Dithering and Phase
« Reply #8 on: January 18, 2006, 12:42:06 PM »

dcollins wrote on Wed, 18 January 2006 02:44

Ronny wrote on Tue, 17 January 2006 23:26


I've always wondered about that. I read in a manual or two that dithering increases dynamic range by around -10dB.



And they would be wrong.

What dither actually does is to make digital systems work just like analog ones.......

This must have been in a book, somewhere, by now.

Quote:


I thought that they meant perceived gain not actual gain measured inside a system, like what Waves says about IDR making the final 16 bit perceived more like 19 bits of resolution.



Although you may either have to stick your head in the speaker, or have a very quiet room, to hear differences at the LSB.

Quote:


I'm not saying that I agree with them, but I've seen Digicheck show -107dB when inputting a  32 bit dithered to 16 bit signal. Can anyone explain what's happening here?



If your meter is right, then the amplitude is wrong.  Do you have it set to 18 bit?

DC






Yep, that's what I thought.

I've checked Digicheck analysis and meters with others and I feel that they are accurate to 1/100th dB. I double checked the dithered output and it was 16 bit. Obviously I made a mistake somewhere, or perhaps the console was outputting 18 bit when it was set on 16. I really can't say where I screwed up or where the malfunction was, but I'll recheck when I get time.  
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