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Data Loss On Low Level Signals
Old 6th January 2019
  #1
Gear Head
Data Loss On Low Level Signals

Hello good folks...

Recently I've noticed a strange issue when bouncing down low volume stems or sounds after processing.

Here's a screenshot the original sound. For what it's worth, it's a single mallet hit rendered through Ableton Live, as seen in Sony Sound Forge 9.0 - 44khz/32bit undithered.

This is that same sound zoomed in to the max, vertically. There's a nice and smooth fade at the end of the waveform all the way down to infinity, right? Cool.

Now, let's do some processing...

Here I've run it through VVV, at 50% wet with a decay of about 10 seconds.

First there's nothing unusual, but let's zoom in again... Now what the heck is happening to the very end of the tail? For what it's worth, the sound was rendered at 44khz/32bit undithered again, no downsampling or shortening of the word length.

Here's the same shot zoomed in even further at the point of the signal disappearing.

So what's happening here?

Some points:

1) It's not just Valhalla VintageVerb, I can replicate this weirdness with a large variety of other processors.

2) Doesn't seem to be Ableton Live either, the same thing happens when doing all this through REAPER
EDIT: Actually no, I remember wrong. I reprocessed it through REAPER with the exact same settings and it turns out everything is a-okay, doing that in REAPER and the tail goes on for 20 more seconds than in Ableton Live...

So what's Ableton doing here internally?

My audio interface is the old and trusty M-Audio Audiophile 2496 PCI card... Running 64bit Windows 10 Pro and 64bit Ableton Live.

Many thanks to anyone willing to help and shed some light on this!

Last edited by mrgs; 6th January 2019 at 05:22 PM.. Reason: 1) Added info, 2) Formatting
Old 6th January 2019
  #2
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stinkyfingers's Avatar
 

could you post a sample file ?
Old 6th January 2019
  #3
Gear Head
Quote:
Originally Posted by stinkyfingers View Post
could you post a sample file ?
Here you go. The unprocessed and processed files shown above.
Old 6th January 2019
  #4
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i'm no reverb expert but it seems normal to me...the source signal has completely decayed and the reverb decay is still going. depending on the algorithm, the decay may or may not be "smooth".
Old 6th January 2019
  #5
Gear Head
Quote:
Originally Posted by stinkyfingers View Post
i'm no reverb expert but it seems normal to me...the source signal has completely decayed and the reverb decay is still going. depending on the algorithm, the decay may or may not be "smooth".
Thanks for your help kindly, but that's not the case at all.

I just edited my original post as I re-did the processing with REAPER, and it doesn't happen there. It's Concert Hall algo on the NOW mode by the way. And here's the reprocessed WAV, too: Download

So the data loss must be occurring inside Ableton Live, but... how?

EDIT: By the way, this issue doesn't seem to be restricted to time-domain effects only. From what I remember, this can happen with various other processors as well. For example if there's a really low-level tail fade already present in the file, I process it with some third party effects inside Ableton, bounce it down - and blam, the tail first gets this faulty transmission look and then gets eaten completely after reaching a certain threshold.

Last edited by mrgs; 6th January 2019 at 05:27 PM.. Reason: Added a point
Old 6th January 2019
  #6
Gear Head
Update...

Might be something to do with the internal bit truncation, as I've learned from this crosspost to reddit

Again, why is this happening? Shouldn't the noise floor of 32bit audio be way lower than around where it drops out in my case? And why does it happen in Ableton Live but not REAPER?
Old 6th January 2019
  #7
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12ax7's Avatar
 

Quote:
Originally Posted by mrgs View Post
I re-did the processing with REAPER, and it doesn't happen there.
There's your cure right there.
Old 7th January 2019
  #8
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stinkyfingers's Avatar
 

I took a look at the file, it is not truncation, the audio is “dropping out”.
The duration of drop outs are multiples of window/buffer sizes (2048,4096,8192).
No idea what would cause that...pdc or something ?
Old 7th January 2019
  #9
Gear Head
Quote:
Originally Posted by stinkyfingers View Post
I took a look at the file, it is not truncation, the audio is “dropping out”.
The duration of drop outs are multiples of window/buffer sizes (2048,4096,8192).
No idea what would cause that...pdc or something ?
It happens with PDC toggled off, too.

With that thread at r/audioengineering going on further, the conclusion seems to be that it's probably to do with preventing denormalization... Why the folks at Ableton decided that gating everything below -100db is the best way to do it though is beyond me.

Really going to have to dump Live and move over to REAPER, I guess

It looks freakin' scary though.
Old 7th January 2019
  #10
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stinkyfingers's Avatar
 

In between the “drop outs” there are sample values well below -100 dBFS...so there is no “gating” or truncation at that level.
I think the duration of the drop outs should be a decent clue...
Old 7th January 2019
  #11
Gear Head
Quote:
Originally Posted by stinkyfingers View Post
In between the “drop outs” there are sample values well below -100 dBFS...so there is no “gating” or truncation at that level.
I think the duration of the drop outs should be a decent clue...
True, that's a good point... It doesn't seem to be PDC though, do you have any other ideas what it could entail? (The fact that the dropouts are multiples of buffer/window sizes)
Old 7th January 2019
  #12
Gear Head
Something I just did... I threw a 0db slab of unprocessed white noise at Live, lowered the signal to -99db in DMG TrackControl (nothing else on the inserts) and rendered that out. I zoomed in and the signal is all there, waveform and all, lowered to -99db.

Then I took it again and lowered it down to -100db and rendered it out and it's all gone, nada, no waveform, nothing. So that means Ableton Live simply starts ignoring buffers that fall below -100db?

And that happens with a freakin' utility plugin, not reverbs or delays or whatever.

By the way, it doesn't happen with Ableton Live's stock plugins, only with the third party ones for some reason.

So what that means to the user is if they're using third party plugins in Live, they're back to 16bit level basically. No matter what
Old 7th January 2019
  #13
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you know, i wouldn't have believed you if i didn't just download the demo and confirm that some dumb **** is happening in the effects path...
(just briefly checked it out so i can't say exactly what, but it's not "right")
Old 7th January 2019
  #14
Gear Head
Thanks to an idea from Chris (Airwindows), I did develop a workaround to this though...

Before hitting the reverb or whatever third party plugin with my sounds, I will run a -96db DC offset signal into it along with the sounds themselves... Then once it's been bounced down, I will remove the DC offset from the stem and everything's alright, I will have a beautiful tail to the sound, no dropouts. So it's kinda possible to fool Ableton Live, as the signal never really drops below -100db

Just cutting anything below -100db seems to be the most tremendously stupid way to save up on processing power though (assuming this is what's happening here)

EDIT:

Found a less tedious way around this actually... As long as I have this chain on every track, this cannot happen
Old 8th January 2019
  #15
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Is this a known issue in the Ableton community ?
If not, it should be...
I don’t even use live and this bothers me.
Old 8th January 2019
  #16
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zvukofor's Avatar
Quote:
Originally Posted by stinkyfingers View Post
Is this a known issue in the Ableton community ?
If not, it should be...
I don’t even use live and this bothers me.
Yeap, need to know is it a consistent Ableton live behavior... i do not use Live either, but almost all of my clients-musicians use it...
Old 8th January 2019
  #17
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stinkyfingers's Avatar
 

Quote:
Originally Posted by mrgs View Post
Found a less tedious way around this actually... As long as I have this chain on every track, this cannot happen
...unless you have an effect in the chain that removes DC (ie...anything with HPF)
DC can also have a significant impact on non-linear effects processing, which may be good or bad.
Old 8th January 2019
  #18
Gear Head
Quote:
Originally Posted by stinkyfingers View Post
Is this a known issue in the Ableton community ?
If not, it should be...
I don’t even use live and this bothers me.
I've been aware of it since Live 9, I've just never had the time or energy to make a post about it and prove that to someone... If you hadn't tried it yourself, even you wouldn't have believed me, right? And there's a lot of sensitivity on the internet in regards to Ableton Live, due to the rumours of it's "inferior sound engine", so it's rather hard to press something like that through to the community... So far, I've searched for answers, yet never found anyone else noticing the issue.

EDIT: I have posted this to r/ableton on Reddit now though.

Quote:
Originally Posted by stinkyfingers View Post
...unless you have an effect in the chain that removes DC (ie...anything with HPF)
DC can also have a significant impact on non-linear effects processing, which may be good or bad.
Yeah, the little blue (engaged) DC button on the last utility plugin does exactly that. Although I am aware of the fact that if I were to place some largely level dependent stuff in place of the reverb (like something that's designed to emulate analog hardware, like Nebula or whatever), the DC passing through that will mess with the signal, at least to the level of the end result being different than it would be without the DC...
Old 8th January 2019
  #19
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here's one example from me...to publicly confirm the issue.
(44.1kHz/32bf project & files)

i imported a 441 Hz sine wave @ 0 dBFS & -6 dBFS (toggles) into live 10 and lowered the gain with DMG EQuilibrium output fader to "-99.99" dBFS. i hit play and captured the output via Reaper/Soundflower. here are some pics of what happened...

source file >
https://i.imgur.com/wpMFwZ5.png

ableton live output > (32 bit stream)
https://i.imgur.com/LPgnrhX.png

zoom 1 > "drop out" >
https://i.imgur.com/QiCL30O.png

zoom 2 > "drop in" >
https://i.imgur.com/PJTbYnP.png

zoom 3 > weird **** before a "drop out"
https://i.imgur.com/XlWUHNu.png

if this isn't a bug...uh...
Old 8th January 2019
  #20
Gear Head
Quote:
Originally Posted by stinkyfingers View Post
here's one example from me...to publicly confirm the issue.
(44.1kHz/32bf project & files)

i imported a 441 Hz sine wave @ 0 dBFS & -6 dBFS (toggles) into live and lowered the gain with DMG EQuilibrium output fader to "-99.99" dBFS. i hit play and captured the output via Reaper/Soundflower. here are some pics of what happened...

source file >
https://i.imgur.com/wpMFwZ5.png

ableton live output >
https://i.imgur.com/LPgnrhX.png

zoom 1 > "drop out" >
https://i.imgur.com/QiCL30O.png

zoom 2 > "drop in" >
https://i.imgur.com/PJTbYnP.png

zoom 3 > weird **** before a "drop out"
https://i.imgur.com/XlWUHNu.png

important to note that there are sample values below -100 in between "drop outs"...(ie...still 32 bf).

if this isn't a bug...uh...
Thanks for verifying and posting examples!

I don't know if that's a bug or intentional behavior... I also asked a rather well known DSP developer to observe this and he was kind enough to take a look, even though he's not involved with Ableton... Since it's a private message, I feel uncomfortable disclosing who exactly it was, but here's what they had to say:

Quote:
If the dropouts are entire buffers that's telling me the following: Live is actively looking for places to suspend processing and gate the signal. I'd be curious whether anything's being processed at all during the dropouts, certainly it'll be leaving the dropouts out of further processing.

I think it's not denormalization, I think it's 'save CPU by ignoring buffers where the loudest sample is too low level'.
So it may not even be a bug?

Anyway, I did post this to the Ableton community on reddit, the few answers I've got on this so far make me wonder why TF am I bothering at all...
Old 8th January 2019
  #21
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stinkyfingers's Avatar
 

i linked to this thread in the "ableton sound quality" thread here, where there are pages and pages of people insisting that all DAWs are exactly the same...
Old 8th January 2019
  #22
Gear Head
Yeh, it's been a foul discussion that I've never wanted to get involved in though... If this never gets fixed or explained by or even looked at by the team at Ableton, I at least hope this thread will serve as replicable proof and testament to the fact that no, all DAWS are not the same seemingly. At least when it comes to processing beneath -100db with third party plugins
Old 9th January 2019
  #23
Gear Maniac
 

Just wanted to chime in to also further verify what's been discovered here...

I tested with a Sine Generator set to 0 db and used Airwindows BitshiftGain to lower the signal by 16 Bits and then raise it again by 16 Bits. As you can see in the screenshots, when i then lowered the Sine Wave by 3.68 db, the Audio disappears. At -3.67 db, it's there...
So... It seems we get around 16 1/2 Bits dynamic range in Ableton Live (10.0.5) when processing with Plugins.
Question is: Does this matter sonically? When working in 24 Bit, I guess we still have the benefit of the lower noise floor. When my final product is in 16 Bit, it doesn't matter anyway. But if my final format would be 24 Bit?
Hmmm...
Attached Thumbnails
Data Loss On Low Level Signals-screenshot-5-.jpg   Data Loss On Low Level Signals-screenshot-6-.jpg  
Old 9th January 2019
  #24
Gear Head
Quote:
Originally Posted by Fishmac View Post
Question is: Does this matter sonically? When working in 24 Bit, I guess we still have the benefit of the lower noise floor. When my final product is in 16 Bit, it doesn't matter anyway. But if my final format would be 24 Bit?
Hmmm...
My biggest gripe is when I want to bring the stuff that dropped below -100db back up dramatically in the mixing stage, I can no longer do it, cause it's gone.
Old 9th January 2019
  #25
Gear Maniac
 

Quote:
Originally Posted by mrgs View Post
My biggest gripe is when I want to bring the stuff that dropped below -100db back up dramatically in the mixing stage, I can no longer do it, cause it's gone.
That's true! I just wrote Abletons Tech Support, explained the matter and asked for a solution. I mean, when I work in 24 Bits, i want 24 Bits, right?
Old 9th January 2019
  #26
Gear Head
Quote:
Originally Posted by Fishmac View Post
That's true! I just wrote Abletons Tech Support, explained the matter and asked for a solution. I mean, when I work in 24 Bits, i want 24 Bits, right?
Precisely
Old 9th January 2019
  #27
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Just out of curiosity, are there any settings to get a lower range for the track faders/automation ?
Like...can you actually use values lower than -70 dBFS or is that the limit ?
Old 9th January 2019
  #28
Gear Maniac
 

That's the limit for the faders. If you want more, you'd have to use the utility effect and use it's gain in addition.
Old 9th January 2019
  #29
Gear Head
Quote:
Originally Posted by Fishmac View Post
That's the limit for the faders. If you want more, you'd have to use the utility effect and use it's gain in addition.
That ain't going below -70db either, so you gotta stack them I just use the free DMG TrackControl instead of that usually though.

By the way, please let us know if you get any feedback from the tech support!
Old 9th January 2019
  #30
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I can get about -139 dBFS with the fader + utility...
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