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Inter-sample peaks & headroom

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Inter-sample peaks & headroom

Postby PianoPerson » Thu Jul 31, 2014 8:23 am

I was very interested to read about the additional 3.5 dB headroom that Benchmark built into their DAC2 to accommodate inter-sample peaks on commercial CDs.

I'm wondering how this is different from simply attenuating a signal by 3.5 dB prior to DA-conversion.

If, for example, I attenuate an incoming Spdif signal from a CD-player by 3.5 dB in RME's TotalMix, am I not doing the same thing, and won't the slight reduction in bit depth be inaudible? What am I missing here?
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Re: Inter-sample peaks & headroom

Postby Hugh Robjohns » Thu Jul 31, 2014 9:18 am

PianoPerson wrote:I'm wondering how this is different from simply attenuating a signal by 3.5 dB prior to DA-conversion.

There is no difference, and that's exactly what I've been doing for years. It can make a surprisingly big difference in quality with badly mastered material, too.

If, for example, I attenuate an incoming Spdif signal from a CD-player by 3.5 dB in RME's TotalMix, am I not doing the same thing

Yes. That would work fine.

I have my (CD) music playing systems set up to attenuate by 6dB because it's an easier number to work with (it's just a single bit shift) and it absolutely guarantees no intersample clipping is ever possible, but I've never seen more than +3dBFS in commercial mixers, so 3.5dB works for everything in practice.

...and won't the slight reduction in bit depth be inaudible? What am I missing here?

All modern digital interfaces handle 24 bits but a CD source only sends 16 bits, so applying a 6dB attenuation simply means the CD signal occupies bits 2-17 instead of 1-16. The original CD dither signal moves with it and there is no audio data being lopped off the bottom, so it's all good.

If you are working with a monitoring system optimised for a sensible headroom margin then you might find it beneficial to attenuate CD reference sources by 12dB to bring them more in line with the typical loudness of locally mixed material and projects in progress.

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Re: Inter-sample peaks & headroom

Postby ef37a » Thu Jul 31, 2014 11:19 am

Bump.

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Re: Inter-sample peaks & headroom

Postby Hugh Robjohns » Thu Jul 31, 2014 11:54 am

Why are you bumping something posted just three hours ago?

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Re: Inter-sample peaks & headroom

Postby PianoPerson » Thu Jul 31, 2014 12:19 pm

Thanks for this lucid explanation, Hugh!

So the 3.5 dB additional headroom isn't really a reason in itself to purchase the DAC2, as long as you're able to attenuate a CD signal in other ways (although it can make a big difference if you feed CD signals directly into the DAC2).

I suppose that for DA-converters with a digital volume control, like the Violectric V800, you can use a similar trick by making sure its output is always turned down a few notches before it's sent to, say, a monitor controller like the SPL 2Control. That actually sounds like a really nice system and it's quite a bit cheaper than the DAC2 (although I'm sure the DAC2 is a fantastic converter).

The whole inter-sample peak issue seems a fairly powerful argument in favour of digital volume controls.
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Re: Inter-sample peaks & headroom

Postby PianoPerson » Thu Jul 31, 2014 12:28 pm

P.S. I've been amazed how utterly horrible some commercial CDs can sound on proper speakers ever since I bought a pair of PSI Audio A17M speakers 2-3 years ago. They're REALLY unforgiving speakers but for example virtually all ECM releases sound glorious on them. ECM doesn't take part in any loudness wars and I'm pretty sure most of their CDs peak at no more than -3.0 dB. It all makes sense.
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Re: Inter-sample peaks & headroom

Postby ef37a » Thu Jul 31, 2014 12:52 pm

Hugh Robjohns wrote:Why are you bumping something posted just three hours ago?

H

Because I want to "keep in the loop"?
Bit "wrong side of bed" today isn't it?

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Re: Inter-sample peaks & headroom

Postby Hugh Robjohns » Thu Jul 31, 2014 1:07 pm

PianoPerson wrote:So the 3.5 dB additional headroom isn't really a reason in itself to purchase the DAC2, as long as you're able to attenuate a CD signal in other ways (although it can make a big difference if you feed CD signals directly into the DAC2).

The DAC2 is a superb converter, and the headroom management is just one aspect of why it sounds as good as it does -- but it is something that is fairly easy to replicate with obvious audible benefits in other systems.

The whole inter-sample peak issue seems a fairly powerful argument in favour of digital volume controls.

Yes, provided the gain control algorithm is done properly, which isn't difficult.

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Re: Inter-sample peaks & headroom

Postby Hugh Robjohns » Thu Jul 31, 2014 1:09 pm

ef37a wrote:Because I want to "keep in the loop"?

Adding the thread to your favourites using the 'add thread to my favourites' is probably a better way.

Bit "wrong side of bed" today isn't it?

Not at all. It just seemed a pointlessly odd thing to do.

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Re: Inter-sample peaks & headroom

Postby ef37a » Thu Jul 31, 2014 1:21 pm

Hugh Robjohns wrote:
ef37a wrote:Because I want to "keep in the loop"?

Adding the thread to your favourites using the 'add thread to my favourites' is probably a better way.

Bit "wrong side of bed" today isn't it?

Not at all. It just seemed a pointlessly odd thing to do.

H

I have "bumped" quite few time here and in several other forums when I have nothing to contribute at the time, maybe never but wish to learn!
Never has anyone oddly or pointlessly mentioned it!

I shall use "Bazinga" henceforth.

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Re: Inter-sample peaks & headroom

Postby Hugh Robjohns » Thu Jul 31, 2014 1:57 pm

ef37a wrote:I have "bumped" quite few time here...


yes, I know... which is why I thought I should it about time I raised this odd behaviour with you.

...when I have nothing to contribute at the time, maybe never but wish to learn!


If you have nothing to contribute, why contribute? And if there's nothing new you're not going to learn anything either!

If a potentially interesting or important post/thread has been missed and gone unanswered for a few days, bumping it back up to receive fresh attention makes some sense. But there is no sense at all in 'bumping' a post which is only a matter of hours old, still prominent on the first page of the active topics list, and which has already received a pretty comprehensive reply!

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Re: Inter-sample peaks & headroom

Postby alexis » Thu Jul 31, 2014 2:04 pm

Hugh, after reading your replies above re: playing back CDs at 3-6 dBFS below peak to avoid intersample clipping, I wonder if you advocate a similar approach when actually rendering to disk/.wav etc. in a DAW - i.e., keeping the digital peak on the master fader no higher than 3 (or 6?) dBFS below peak when exporting?

Thanks -
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Re: Inter-sample peaks & headroom

Postby Hugh Robjohns » Thu Jul 31, 2014 2:21 pm

alexis wrote:Hugh, after reading your replies above re: playing back CDs at 3-6 dBFS below peak to avoid intersample clipping,...


Intersample clipping can only occur when the waveform is being reconstructed, either in a D-A or in any process which involves oversampling or up sampling (so SRC processes, plug-in effects that involve up-sampling, etc)

I wonder if you advocate a similar approach when actually rendering to disk/.wav etc. in a DAW - i.e., keeping the digital peak on the master fader no higher than 3 (or 6?) dBFS below peak when exporting?


I advocate the maintenance of a sensible headroom margin at all times, so yes. But in a simple export there is no waveform reconstruction going on, so peak level samples aren't a problem in themselves and no further data corruption can occur.

The new loudness normalisation standard (ITU-R BS.1770-3) requires peak signal levels to be determined with a True Peak meter (which uses oversampling to better reconstruct the actual waveform), and that the measured true peaks never go above -1dBTP. The EBU spec calls for nothing higher than -3dBTP.

If using ordinary DAW-style sample-peak meters, and when applying lots of limiting or compression, I wouldn't want to risk going higher than -6dBFS, or -3dBFS if using only a little limiting/compression.

But True Peak meters are the way top go if you are worried about intersample peaks, and nothing ever higher than -1dBTP.

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Re: Inter-sample peaks & headroom

Postby ef37a » Thu Jul 31, 2014 2:40 pm

Hugh Robjohns wrote:
ef37a wrote:I have "bumped" quite few time here...

yes, I know... which is why I thought I should it about time I raised this odd behaviour with you.

...when I have nothing to contribute at the time, maybe never but wish to learn!

If you have nothing to contribute, why contribute? And if there's nothing new you're not going to learn anything either!

If a potentially interesting or important post/thread has been missed and gone unanswered for a few days, bumping it back up to receive fresh attention makes some sense. But there is no sense at all in 'bumping' a post which is only a matter of hours old, still prominent on the first page of the active topics list, and which has already received a pretty comprehensive reply!

H

*&%$£! You are annoying sometimes Sheldon!

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Re: Inter-sample peaks & headroom

Postby PianoPerson » Thu Jul 31, 2014 2:53 pm

Actually, it is you who is being annoying, Dave. Almost half of this thread has been wasted on your pointless and uncivil posts. It's very irritating.
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Re: Inter-sample peaks & headroom

Postby alexis » Thu Jul 31, 2014 3:46 pm

Hugh Robjohns wrote:
alexis wrote:Hugh, after reading your replies above re: playing back CDs at 3-6 dBFS below peak to avoid intersample clipping,...

Intersample clipping can only occur when the waveform is being reconstructed, either in a D-A or in any process which involves oversampling or up sampling (so SRC processes, plug-in effects that involve up-sampling, etc)

I wonder if you advocate a similar approach when actually rendering to disk/.wav etc. in a DAW - i.e., keeping the digital peak on the master fader no higher than 3 (or 6?) dBFS below peak when exporting?

I advocate the maintenance of a sensible headroom margin at all times, so yes. But in a simple export there is no waveform reconstruction going on, so peak level samples aren't a problem in themselves and no further data corruption can occur.

The new loudness normalisation standard (ITU-R BS.1770-3) requires peak signal levels to be determined with a True Peak meter (which uses oversampling to better reconstruct the actual waveform), and that the measured true peaks never go above -1dBTP. The EBU spec calls for nothing higher than -3dBTP.

If using ordinary DAW-style sample-peak meters, and when applying lots of limiting or compression, I wouldn't want to risk going higher than -6dBFS, or -3dBFS if using only a little limiting/compression.

But True Peak meters are the way top go if you are worried about intersample peaks, and nothing ever higher than -1dBTP.

H


Thank you, Hugh.

Cubase 7.5.20 has a new meter function I am just getting acquainted with - I see it has LU/LUFS, true peak, and a bunch of other things I'm not familiar with that I didn't see specific discussion of in your excellent SOS a few months back. But at least I'll be looking at LU/LUFS and true peak, which is more than I did before.

Thanks again -
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Re: Inter-sample peaks & headroom

Postby narcoman » Thu Jul 31, 2014 3:54 pm

PianoPerson wrote:Actually, it is you who is being annoying, Dave. Almost half of this thread has been wasted on your pointless and uncivil posts. It's very irritating.

Forums, like any other social space, have long standing friendships, in jokes and other such malarky's. Dont scold until you understand the ins and outs!!
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Re: Inter-sample peaks & headroom

Postby ef37a » Thu Jul 31, 2014 4:34 pm

PianoPerson wrote:Actually, it is you who is being annoying, Dave. Almost half of this thread has been wasted on your pointless and uncivil posts. It's very irritating.

Nope. All he had to do was let it lie as it has other times and other places.

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Re: Inter-sample peaks & headroom

Postby ef37a » Thu Jul 31, 2014 4:36 pm

narcoman wrote:
PianoPerson wrote:Actually, it is you who is being annoying, Dave. Almost half of this thread has been wasted on your pointless and uncivil posts. It's very irritating.

Forums, like any other social space, have long standing friendships, in jokes and other such malarky's. Dont scold until you understand the ins and outs!!

Not sure who is scolding who there Narcs!

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Re: Inter-sample peaks & headroom

Postby Hugh Robjohns » Thu Jul 31, 2014 4:37 pm

alexis wrote:Cubase 7.5.20 has a new meter function I am just getting acquainted with - I see it has LU/LUFS, true peak, and a bunch of other things I'm not familiar with that I didn't see specific discussion of in your excellent SOS a few months back.

It was all in there, and conveniently highlighted in the coloured boxes at the end of the online article:

http://www.soundonsound.com/sos/feb14/a ... ss-war.htm

But at least I'll be looking at LU/LUFS and true peak, which is more than I did before.

Good man! Cubase is a designed in Germany and hence used LUFS, but as an American you're allowed to refer to LKFS instead...

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Re: Inter-sample peaks & headroom

Postby Hugh Robjohns » Thu Jul 31, 2014 4:39 pm

ef37a wrote:All he had to do was let it lie as it has other times and other places.

... but that way you'll never learn ... and you've already said that's something you're keen about!

But hey, it's no biggie, just a matter of netiquette.

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Re: Inter-sample peaks & headroom

Postby ef37a » Thu Jul 31, 2014 4:48 pm

Hugh Robjohns wrote:But hey, it's no biggie, just a matter of netiquette


Seems to be a biggie to you. You HAD to tell me off didn't you?

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Re: Inter-sample peaks & headroom

Postby Hugh Robjohns » Thu Jul 31, 2014 5:07 pm

ef37a wrote:You HAD to tell me off didn't you?

You certainly seem to be taking it that way!

(apologies for appearing to edit your post -- I accidentally hit edit rather than quote)

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Re: Inter-sample peaks & headroom

Postby Zukan » Fri Aug 01, 2014 6:10 am

Dave, I'm good at spanking and cheap with it. I even wear things. Call me for rates. We deal only in Minstrels.
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Re: Inter-sample peaks & headroom

Postby shufflebeat » Fri Aug 01, 2014 7:13 am

Minstrels have been 10 to the Hobnob recently. You are cheap, I may have some work for you.
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Re: Inter-sample peaks & headroom

Postby Zukan » Fri Aug 01, 2014 7:17 am

Hobnobs are so yesterday. Keep up with the times FFS.
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Re: Inter-sample peaks & headroom

Postby shufflebeat » Sat Aug 16, 2014 1:22 am

This is a temporary economic trend and I urge everyone to stock up in anticipation of an upturn.

I have some melted down into bars as a little nest-egg instead of a costly pension scheme.
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Re: Inter-sample peaks & headroom

Postby Zukan » Mon Aug 18, 2014 7:15 am

Bastard! So it was you who cornered the market with that last gasp bidding war?
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