Intersample peaks - is it an issue?
May 11, 2015 at 10:02 AM Thread Starter Post #1 of 45

MacacoDoSom

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Most CDs have 0 Db FS witch most of the time results in having intersample peaks (TP) of +2/+3 dB, would this be an issue with most modern DACs? or they always have enough headroom to to fit these? and about the amplifier?
any thoughts?
 
May 11, 2015 at 10:11 AM Post #2 of 45

stv014

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Some DACs (like the CS4398 on this sound card, which clips only at about +2 dBFS) have headroom for them, but not others. Although with music, it is difficult to hear the difference, because for inter-sample peaks above 0 dBFS to occur in significant numbers, it has to be mastered pretty badly in the first place, and the slight additional clipping is likely to be masked. With synthetic test signals, it can be made easily audible, as shown here. In any case, those who are worried about this can always just set -2 dB or lower digital volume.
 
May 11, 2015 at 10:24 AM Post #3 of 45

MacacoDoSom

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  Some DACs (like the CS4398 on this sound card, which clips only at about +2 dBFS) have headroom for them, but not others. Although with music, it is difficult to hear the difference, because for inter-sample peaks above 0 dBFS to occur in significant numbers, it has to be mastered pretty badly in the first place, and the slight additional clipping is likely to be masked. With synthetic test signals, it can be made easily audible, as shown here. In any case, those who are worried about this can always just set -2 dB or lower digital volume.


thank you for your reply. There is apparently the issue when ripping CDs to a lossy format...
I have ripped a CD sometime ago (will try to find it) that had +5.something and hadn't noticing any distortion when played in a CD player or in my PC with an external DAC ( a Presonus Firestudio Project and a Roland UA-55) only noticed some strange distortion when I heard the lossy result (wma 256k)...
 
There seems to be a trend now to control these TPs in the studio, but sometime ago no one ever bothered about it, if it's -0.2 dB FS it was good... and nobody talked about it...
 
May 11, 2015 at 10:46 AM Post #4 of 45

stv014

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By the way, the signal I used in the test from the second link can be generated with the testgen utility using this input file (for 44100 Hz sample rate):
 
Code:
 sine 0 5 11025 45 0.82842 0.82842 sine 0 5 15025 0 0.41421 0.41421
 
Or use any other software to create it (the parameters after 'sine 0 5' are the frequency, phase, and left/right level). This plays at slightly less than +2 dBFS, and if the DAC cannot handle it at full digital volume, it will produce audible intermodulation and possibly aliasing. These are very loud high frequency tones, so it is recommended to listen at a low analog volume and for a short time.
 
May 11, 2015 at 1:19 PM Post #6 of 45

bigshot

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I've found that iTunes boosts the level a hair when it converts to AAC. If a track is normalized all the way up to the edge, the AAC can end up clipping. The solution to that is to lower the volume a hair in a sound editing program before converting to AAC. I don't run into a problem with that much, because the CDs I'm ripping usually are well mastered and aren't compressed up to as loud as possible like that.
 
May 11, 2015 at 2:24 PM Post #7 of 45

MacacoDoSom

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  I've found that iTunes boosts the level a hair when it converts to AAC. If a track is normalized all the way up to the edge, the AAC can end up clipping. The solution to that is to lower the volume a hair in a sound editing program before converting to AAC. I don't run into a problem with that much, because the CDs I'm ripping usually are well mastered and aren't compressed up to as loud as possible like that.

...just an example...I'm trying to find many more that I know that I have but cannot remember...
 
strangely enough this is not in the 1st track that has a massive distortion... it's in a ballad (track 8)
 
I think that this was their intention...

ZZ Top La futura mastered by Vlado Meller
 
'senior mastering engineer at Vlado Meller Mastering in Charleston, South Carolina. He has won two Grammy Awards' (wikipedia)
 

 
 
------------------------------------------------------------------
Measurement date  :11 May 2015 19:08:30

settings overview :
  meter type            : ITU-R BS.1770-2: "True-Peak" Level
  over level      (dBTP): 0
  reference level (dBFS): 0
result summary:
  1001 OVERS, max: L (+2.72 dB)    R (+3.05 dB)
------------------------------------------------------------------
 
and a more conservative one... Oregon - Beyond Words (Chesky Records)
 
------------------------------------------------------------------
Measurement date  :11 May 2015 19:47:03

settings overview :
  meter type            : ITU-R BS.1770-2: "True-Peak" Level
  over level      (dBTP): 0
  reference level (dBFS): 0
result summary:
  15 OVERS, max: L (+1.64 dB)    R (+1.10 dB)
------------------------------------------------------------------
 
 

 
May 11, 2015 at 4:32 PM Post #9 of 45

MacacoDoSom

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  I was going to ask about that audio tool you were using, but the price tag is way out of my range. ($1200! USD)


Well the RX4 does the same and is 'only' $349...
 
you can try PPMulator demo
 
or Orban loudness meter...Free
 
Or a vst with foobar, there some free, the drawback is that they show you the info in realtime...
 
May 11, 2015 at 8:09 PM Post #11 of 45

bigshot

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Well, I don't listen to a lot of hyper compressed hot mastered music, so it really isn't an issue for me. If it was, I'd just rip to WAV, batch process them down a DB, then convert to lossy.
 
May 12, 2015 at 12:28 AM Post #12 of 45

dprimary

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I would not want to release anything with with inter-sample peaks over 0. It could cause problems with codecs, streaming, radio at the very least considering the amount of devices I hear that seem to be distorting at 0dB I would say it is common.
 
May 12, 2015 at 3:41 AM Post #13 of 45

MacacoDoSom

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  I would not want to release anything with with inter-sample peaks over 0. It could cause problems with codecs, streaming, radio at the very least considering the amount of devices I hear that seem to be distorting at 0dB I would say it is common.

That's the point for me, but it seems that almost all the major labels (and not only) suffer from this issue on CD and 44.1 files, only the so called HD files don't usually have it (or have it in a much small degree) because they would be clipped in FS... but these are usually for a market niche...
The (mostly) small radio stations have to spend money to adhere  to the new loudness norms... 
The average consumer, or doesn't notice anything or thinks it's a bad recording/master and buys HD files.........uhmmmm.....
Loudness WARS?????
 
May 12, 2015 at 11:48 PM Post #14 of 45

castleofargh

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I've noticed some clipping, mostly on a few mp3s somehow. not knowing what it was, at first I just checked the "avoid clipping"  in foobar, but that didn't seem to solve the problem which led me to think it was maybe on the DAC side. trying 2 DACs didn't felt kind of different but didn't solve the problem(maybe different upsampling, one having async USB? or whatever, IDK). I still had some minor clipping on a few tracks that shouldn't be there. my solution testing stuff randomly was to put -3db in foobar's preamp ^_^. I tried different values and settled for 3db somehow, guess I got lucky on that one(well -1db still audibly clipped sometimes, -2 felt ok so I played it safe and used -3). and that did the trick, so for a long time I didn't look further into it, using the family telling, "if it works don't F****ing touch it!".
 
and it's the cool guy from JDS lab and some benchmark post on their website that made me realize what it was likely to be maybe 6months ago.
if you want, you can buy the DAC2, and apparently not worry about that anymore.  I find that paying 3db of noise floor is cheaper, but it does look like a pretty cool DAC.
 
May 13, 2015 at 12:04 AM Post #15 of 45

bigshot

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Simple fix, rip to WAV or AIFF, and batch process your normalize down and conversion to lossy version.
 
It isn't the DAC, it's the conversion process boosting the level a half dB or so
 

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