IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
Is Audacity "Lossless"?, Why doesn't Audacity preseve even wav files intact?
canolradd
post Jul 14 2012, 21:07
Post #1





Group: Members
Posts: 8
Joined: 14-July 12
Member No.: 101430



I need to edit many audio files of various formats: wav, ac3, mp2, etc. I need to cut, to append, to insert, etc. But I'm worried about whether Audacity really preserve audio quality or whether it introduces artifacts. In order to test it, I tried this: import an wav file, make no change to the imported track, and export that track to another wav file (same sample rate, etc.). The result wav file is not identical to the original! What's going on? What am I doing wrong?

Forgive me if this is a silly question, but I'm trying to learn...
Go to the top of the page
+Quote Post
saratoga
post Jul 14 2012, 21:10
Post #2





Group: Members
Posts: 4863
Joined: 2-September 02
Member No.: 3264



QUOTE (canolradd @ Jul 14 2012, 16:07) *
I need to edit many audio files of various formats: wav, ac3, mp2, etc. I need to cut, to append, to insert, etc. But I'm worried about whether Audacity really preserve audio quality or whether it introduces artifacts.


This will not be lossless for lossy formats.

QUOTE (canolradd @ Jul 14 2012, 16:07) *
The result wav file is not identical to the original! What's going on? What am I doing wrong?


There are a lot of different ways you can write a wav header. You need to compare the actual PCM data, not the file holding it. Use a tool like foobar2000 to compare the actual audio samples.
Go to the top of the page
+Quote Post
lvqcl
post Jul 14 2012, 21:17
Post #3





Group: Developer
Posts: 3336
Joined: 2-December 07
Member No.: 49183



QUOTE
What's going on?


Audacity re-dithers its output by default.
Go to the top of the page
+Quote Post
mjb2006
post Jul 14 2012, 22:53
Post #4





Group: Members
Posts: 758
Joined: 12-May 06
From: Colorado, USA
Member No.: 30694



QUOTE (lvqcl @ Jul 14 2012, 14:17) *
Audacity re-dithers its output by default.

canolradd, the default settings are for when you're either starting with a different format, applying effects, or combining multiple clips. For the simple case of loading a file, making cut-and-paste edits or adjusting samples manually, then resaving with minimal changes, you want to turn dithering off.

Last I checked, this is how you do it:
Preferences > Quality ... change the High-quality Conversion dither to 'None'
Go to the top of the page
+Quote Post
canolradd
post Jul 14 2012, 23:26
Post #5





Group: Members
Posts: 8
Joined: 14-July 12
Member No.: 101430



Thanks a lot to all of you. Following your advises, I managed to get an identical wav file, except for the header. As much as I need for now.
Go to the top of the page
+Quote Post
EagleScout1998
post Jul 14 2012, 23:59
Post #6





Group: Members
Posts: 273
Joined: 1-October 06
Member No.: 35820



QUOTE
For the simple case of loading a file, making cut-and-paste edits or adjusting samples manually, then resaving with minimal changes, you want to turn dithering off.


I only use Audacity for when I run into those annoying hidden tracks that follow several minutes of silence. I load the source FLAC into Audacity and then use Sound Finder to create labels where the actual songs are (leaving out the silence). Those labels are exported to FLAC. I take it I should turn dithering off for this? Or does it even matter in this case?

This post has been edited by EagleScout1998: Jul 15 2012, 00:00
Go to the top of the page
+Quote Post
mjb2006
post Jul 15 2012, 05:33
Post #7





Group: Members
Posts: 758
Joined: 12-May 06
From: Colorado, USA
Member No.: 30694



I would turn off dithering for doing a simple track split, yes.
Go to the top of the page
+Quote Post
dhromed
post Jul 15 2012, 10:31
Post #8





Group: Members
Posts: 1287
Joined: 16-February 08
From: NL
Member No.: 51347



QUOTE (EagleScout1998 @ Jul 15 2012, 00:59) *
I only use Audacity for when I run into those annoying hidden tracks that follow several minutes of silence.


If you're using foobar2000 then you'll love the Skip silence dsp.
Since for some reason I can't find the component anywhere, I assume it's part of the standard installation?
Go to the top of the page
+Quote Post
EagleScout1998
post Jul 15 2012, 11:56
Post #9





Group: Members
Posts: 273
Joined: 1-October 06
Member No.: 35820



QUOTE (dhromed @ Jul 15 2012, 03:31) *
If you're using foobar2000 then you'll love the Skip silence dsp.


I know about the Skip Silence DSP. dBpoweramp's ripper also has a similar DSP. However, they don't suit my wants. I prefer having separate tracks. Audacity's Sound Finder function is, so far, the easiest way of doing this. It analyzes the file and creates labels where the sound is. I then export those labels to FLAC. This post raised a red flag because, up until I discovered this post, I didn't know about dithering. I had to do some Googling to figure out what this was and I still don't completely understand. From what I can tell, Audacity intentionally adds noise when downsampling audio. Since this, according to lvqcl, is enabled by default, I was concerned whether this was introducing any undesired (albeit inaudible) artifacts in the newly created tracks.

There is still much about Audacity that is above my pay grade.<br>
Go to the top of the page
+Quote Post
DonP
post Jul 15 2012, 13:51
Post #10





Group: Members (Donating)
Posts: 1471
Joined: 11-February 03
From: Vermont
Member No.: 4955



QUOTE (EagleScout1998 @ Jul 14 2012, 18:59) *
. I take it I should turn dithering off for this? Or does it even matter in this case?


Another thing to check, I thought Audacity initially defaults to 32 bit floating point numbers while editing. No need for that if you are just cut and pasting.
Go to the top of the page
+Quote Post
EagleScout1998
post Jul 16 2012, 09:31
Post #11





Group: Members
Posts: 273
Joined: 1-October 06
Member No.: 35820



I feel like an ass hijacking the OP's thread, but since this is related to Audacity....

As an experiment, I imported a FLAC file into Audacity. Without making any edits whatsoever, I exported this file to FLAC. I then used Foobar to compare these two tracks. This was the result:

CODE
Differences found in 1 out of 1 track pairs.

Comparing:
"C:\Users\Anthony Bertorelli\Desktop\FLAC #01.flac"
"C:\Users\Anthony Bertorelli\Desktop\FLAC #02.flac"
Differences found: 42082194 sample(s), starting at 0.0000680 second(s), peak: 0.0003052 at 120.1485714 second(s), 1ch


This would have given me cause for alarm a couple of days ago. Knowing what I know about dithering (which still isn't much), I set it to "None" and repeated the experiment.

CODE
All tracks decoded fine, no differences found.

Comparing:
"C:\Users\Anthony Bertorelli\Desktop\FLAC #01.flac"
"C:\Users\Anthony Bertorelli\Desktop\FLAC #03.flac"
No differences in decoded data found.


For this experiment, I didn't change the Default Sample Format; I left it at 32 bit float. I believe CD audio is 16 bit. Would I be correct in assuming that Audacity "upsamples" (if that's even a word) the imported FLAC file to 32 bit and then "downsamples" it to 16 bit (or 24 bit) upon export? Hence the added dither?
Go to the top of the page
+Quote Post
dumdidum
post Jul 16 2012, 10:22
Post #12





Group: Members
Posts: 57
Joined: 21-January 12
From: Germany
Member No.: 96595



there is a confirmed bug in audacity related to the issue discussed ITT.

From the 2.0.1 release notes:
QUOTE
Dither noise is incorrectly applied by default if exporting to most formats where the bit depth is the same as (or higher than) the project. For example, this occurs if exporting to 16-bit WAV, 16-bit FLAC or MP3 from a 16-bit project. OGG is unaffected. Workarounds: Set "High Quality" dither to "None" in the Quality Preferences.
Go to the top of the page
+Quote Post
Porcus
post Jul 16 2012, 10:37
Post #13





Group: Members
Posts: 1842
Joined: 30-November 06
Member No.: 38207



EagleScout1998: Tried to hack together a cuesheet for that particular track, and set index marks, and embed it to the track? Might be an acceptable compromise?


--------------------
One day in the Year of the Fox came a time remembered well
Go to the top of the page
+Quote Post

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 29th July 2014 - 16:52