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Why does "hiss" roughen when fading out?
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Sir Cecil



Joined: 30 Jul 2011
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PostPosted: Sat Feb 23, 2013 8:11 pm    Post subject: Why does "hiss" roughen when fading out? Reply with quote

I notice that when fading out the trailing hiss at the end of a piece of music imported from CD (fading using either the fade out control or the volumes method), the hiss on the original recording becomes rougher and grittier as it fades out. The hiss being faded (especially towards the latter part of the fade) exhibits a distinct coarseness which is not evident on the original CD track.
Is there a reason or cure for this? It's only noticeable through headphones when monitoring at high levels and isn't noticeable at normal listening levels, but it's annoying to hear when implementing the fade. Thanks.
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Martin Hairer
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PostPosted: Sun Feb 24, 2013 9:15 pm    Post subject: Why does "hiss" roughen when fading out? Reply with quote

The fade really doesn't do anything except for a volume change, so I don't have any explanation for that, sorry… My suspicion though is that if anything it's an artefact of the way CoreAudio handles playback and not a feature of the resulting audio file. Try burning to a CD and playing through a good Hifi system. Regards,

Martin

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Sir Cecil



Joined: 30 Jul 2011
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PostPosted: Sun Feb 24, 2013 11:20 pm    Post subject: Reply with quote

An update on my initial post... it seems the fadeout is exactly as it should be when working on the Amadeus file, but when saving the final edit as an AIFF file, the fadeout shows the effect I mentioned, with the hiss becoming grainy as it fades out.
This is all below normal listening levels and wouldn't be noticeable through speakers for general listening, but at high levels through headphones when monitoring the work one is doing, there is a definite roughness that creeps into the fade when saving the Amadeus file to AIFF.
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Martin Hairer
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PostPosted: Tue Feb 26, 2013 3:47 pm    Post subject: Why does "hiss" roughen when fading out? Reply with quote

Quote:
there is a definite roughness that creeps into the fade when saving the Amadeus file to AIFF.

What *exact* settings do you use when saving to AIFF? Regards,

Martin

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JEGG



Joined: 24 Feb 2007
Posts: 121

PostPosted: Sat Mar 09, 2013 2:25 am    Post subject: Reply with quote

Sir Cecil wrote:
An update on my initial post... it seems the fadeout is exactly as it should be when working on the Amadeus file, but when saving the final edit as an AIFF file, the fadeout shows the effect I mentioned, with the hiss becoming grainy as it fades out.
This is all below normal listening levels and wouldn't be noticeable through speakers for general listening, but at high levels through headphones when monitoring the work one is doing, there is a definite roughness that creeps into the fade when saving the Amadeus file to AIFF.


What you are describing sounds exactly like a truncation issue. Have you or someone before you changed the bit depth from, say, 24 to 16 without applying dither?

If you are working in a DAW that has an internal bit depth of something like 32 int or float, you still must dither appropriately before you save your file, otherwise you are truncating without dither from the working depth of the DAW to the depth of your file.

While this results in constant low level broadband distortion, it can be argued that , depending on the material, the recording may be "self dithered," the problem is still heard on the tails of reverbs and fades to low level-or up from a low level.

Repeated saves, especially when any of them involves a save followed by raising levels, followed by another save increases the severity of the effect.

With AP, you will have to use a plug-in a (a clumsy workaround), or save at 32 bit in AP and use a different application that incorporates dither to save to the required 24 or 16 bit depth.

Perhaps you can get a copy of Bob Katz's book called "Mastering Audio." It's a technical book, but it is an easy read.


Last edited by JEGG on Tue Apr 16, 2013 9:39 pm; edited 1 time in total
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JEGG



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PostPosted: Sat Mar 09, 2013 6:51 pm    Post subject: Reply with quote

Sir Cecil wrote:
An update on my initial post... it seems the fadeout is exactly as it should be when working on the Amadeus file, but when saving the final edit as an AIFF file, the fadeout shows the effect I mentioned, with the hiss becoming grainy as it fades out.


Just to add one more comment: Notice you said the fadeout is exactly as it should be when working on the Amadeus file (presumably playing it back in Amadeus), and when saving the file, and playing back the file, the hiss is grainy. This almost proves my point. Within Amadeus, you are not truncating. The minute you save the file, you have truncated, and if you have not used appropriate dither, your fades will not fade into pleasing, smooth, and preferably stereo noise-rather the fade will be into rocky and crackly breakup noise. (Note that if you re-import the saved file back into Amadeus, it's still going to sound crackly, you've already done the damage.) Finally, know that while dither (noise) is very low in level, the *effects* of no dither are spiky and relatively high in level, and will absolutely be heard when the volume is turned up on fades.

Also a clarification. I mentioned "above -96dBFS" for 16 bit dither. More precisely, the level should be -91dBFS.
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JEGG



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PostPosted: Tue Apr 16, 2013 9:15 pm    Post subject: Reply with quote

sorry, this is another double post of mine-I'm having difficulty with the forum

I have solved the problem-so it shouldn't happen again.

Apologies!
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Sir Cecil



Joined: 30 Jul 2011
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PostPosted: Wed Apr 24, 2013 6:28 am    Post subject: Reply with quote

Thanks for the responses.
I'm only editing files from standard commercial music CDs. I am editing mostly orchestral film soundtrack music, to eliminate unwanted sections and usually to create custom suites.
I import the original CD files to my desktop and then save them via "Join Files" as a single Amadeus File. I save as 44100 Hz, 16 bit.
I then do all my editing/crossfading etc within Amadeus and when the whole thing is complete, I save the file as an AIFF (saving settings read Uncompressed / 16 bit). At some future date I might want to make a lossless file of it, but that hasn't been the case yet. I've been using only Amadeus files for editing, and AIFF format to save the finished project. I then discard the Amadeus file.
Looking at preferences, I see that "Default Format for new files" is set at Sampling Rate: 44100 Hz and Sampling Depth at 32 bit. "Sample Rate Conversion Quality" is set at 5.
I see no instructions about dither or when to apply it in the manual. I'd been told in the past that working on the relatively straightforward 16 bit CD files I'm editing, with levels almost invariably unchanged except during fadeouts/fade-ins, I needn't concern myself about dither.
I should add that I never hear the coarse effect during fade IN. Only when fading OUT. I'm talking of fades of typically around three or four seconds.
Thanks in advance for any further input.
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JEGG



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PostPosted: Sat Apr 27, 2013 6:03 am    Post subject: Reply with quote

Sir Cecil wrote:

I import the original CD files to my desktop and then save them via "Join Files" as a single Amadeus File. I save as 44100 Hz, 16 bit.
I then do all my editing/crossfading etc within Amadeus and when the whole thing is complete,


The moment you apply a fade, smart edit, level change, or any effect, you expand the file in the DAW to 32 bit.

Sir Cecil wrote:
I save the file as an AIFF (saving settings read Uncompressed / 16 bit).


You have just truncated *without dithering,* from 32 float to 16 bit.

Sir Cecil wrote:
At some future date I might want to make a lossless file of it, but that hasn't been the case yet.


You have just created a lossless file. Lossless files are not immune from all sorts of distortion caused by previous and future miss processing, however.

Sir Cecil wrote:

Looking at preferences, I see that "Default Format for new files" is set at Sampling Rate: 44100 Hz and Sampling Depth at 32 bit. "Sample Rate Conversion Quality" is set at 5.


The SCR conversion quality is irrelevant, since you aren't converting sample rate.

Sir Cecil wrote:

I see no instructions about dither or when to apply it in the manual. I'd been told in the past that working on the relatively straightforward 16 bit CD files I'm editing, with levels almost invariably unchanged except during fadeouts/fade-ins, I needn't concern myself about dither.


A major omission from the manual (and from the application). You have been misinformed. I can't see my previous posts at the moment, but I believe I mentioned a book by Bob Katz. Read that. When any processing is done, the entire file is changed-it doesn't matter if it's only one fade or one smart edit.

BTW: the lingo

Generally, "to truncate" means to truncate without dithering.
Generally, "to dither" means to apply dither and then truncate.

AP should have a save box which offers dither, dither type, and for which bit depth. It doesn't have any of that. You'll have to use a plugin, or use a different application for dither. Generally, "triangle" dither is most appropriate for users of this forum.

Always have everything done-especially level changes-done before applying dither. CDs most likely have shaped dither applied. Which is why you should only apply triangle shaped for very moderately shaped dither.

A 16 or 24 bit file re-imported for more work needs to have dither applied again when saving back to 16 or 24 bit.

Often times, a truncation or two will passed on unnoticed, but even so it will be heard on fades, and on tails of naturally occurring or artificial reverb-the tails and stereo image will be deeper, wider, and smoother.
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Sir Cecil



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PostPosted: Sat Apr 27, 2013 10:05 am    Post subject: Reply with quote

Where is any of this in the manual?

Are you saying that when I've done something as simple as edit out a click with smart edit, or faded out a track, I've ended up lowering the sound quality of the entire file? It seems what is being said is that any simple edit or fade of a CD file cannot be properly executed by Amadeus without distortion. What excuse can there be for this?

Martin Hairer said earlier: "The fade really doesn't do anything except for a volume change, so I don't have any explanation for that".
But now it's being said that the fade is indeed having a key influence and changing the entire file, requiring dithering.


Last edited by Sir Cecil on Sat Apr 27, 2013 4:49 pm; edited 1 time in total
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Martin Hairer
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PostPosted: Sat Apr 27, 2013 3:14 pm    Post subject: Why does "hiss" roughen when fading out? Reply with quote

See

http://www.digitalprosound.com/Htm/Articles/April/Trunc_vs_Dither.htm

for a more nuanced point of view. The upshot is that at normal listening levels,
pretty much nobody can possibly hear any difference, which is why I didn't
add this function. Note also that dithering won't magically make your 16bit fading
sound like a 24bit fading, it will just add some small extra noise so the digital
artefacts you currently hear will be "drowned" in a very low-level hiss.

Of course there are plenty of Audio Units available that allow you to apply
dithering if you feel so inclined. Regards,

Martin

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Sir Cecil



Joined: 30 Jul 2011
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PostPosted: Sat Apr 27, 2013 5:05 pm    Post subject: Reply with quote

Thank you for your replies, even though they do worry me.

Please answer me this...


Let's say for simplicity's sake I have opened a single, five-minute CD track in Amadeus.
I then highlight the last five seconds and execute a standard fadeout for the length of the highlighted portion.
I then save the track I've worked on as another Amadeus file.
I then save that amended Amadeus file track as an AIFF file for my library.
In this case, has the WHOLE five-minute file been converted to 32 bit, and then back down to 16 bit? Or has only the five second highlighted/faded portion been through that process, with the un-highlighted part of the file having always remained unchanged at 16bit (and not in need of dither)?

Thanks


Last edited by Sir Cecil on Sat Apr 27, 2013 5:16 pm; edited 1 time in total
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Martin Hairer
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PostPosted: Sat Apr 27, 2013 5:12 pm    Post subject: Why does "hiss" roughen when fading out? Reply with quote

Quote:
In this case, has the WHOLE five-minute file been converted to 32 bit, and then back down to 16 bit?

Yes, but there is no loss *whatsoever* when doing this conversion. It's not like decoding / reencoding an Mp3 file where you really lose data. Regards,

Martin

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Sir Cecil



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PostPosted: Sat Apr 27, 2013 5:26 pm    Post subject: Reply with quote

So in the circumstances above, if dither is applied to the faded Amadeus track prior to making a final save to AIFF, is the entire file dithered, or just the small section that was highlighted and faded?

Thanks for your patience.
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CDJonah



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PostPosted: Sat Apr 27, 2013 5:47 pm    Post subject: Why does "hiss" roughen when fading out? Reply with quote

Not to be obvious but a sixteen bit number that is transferred to 32 bit
will translate back exactly to the same 16-bit number. Why would you
want to add noise?

Chuck


On 4/27/13 12:26 PM, Sir Cecil wrote:
Quote:
So in the circumstances above, if dither is applied to the faded track prior to making a final save to AIFF, is the whole file dithered, or just the small section that was highlighted and faded?

Thanks for your patience.




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