Exporting M4A Lossless from v2.2.1 in Win-7

[edwinn]

Hey guys, I'm working with a user who records his lectures in GarageBand on a Mac, and he uses Audacity (for Mac) to edit them. We've been talking about him using lossless ALAC for his master files, though he's more an academic and not very tech savvy.

I was able to export a file using the M4A file type:

FTIC_(22 kHz)_Export_M4A_AAC_II.png (22.87 KiB) Viewed 978 times

Notice the difference in file sizes in the figure above: 655k CBR vs 1624k using External command line.


It says in the HELP file:

"Currently this slider has no effect with the version of FFmpeg recommended for Windows and Mac. The exported file is always a constant bit rate (CBR) 196 kbps (stereo) or 98 kbps (mono) file."


That's exactly what I got 98 kbps when tested it in VLC player:

FTIC_(22 kHz)_mono.png (12.42 KiB) Viewed 997 times

Then used the EXTERNAL PROGRAM file type and Command Line string to do it right:

FTIC_(22 kHz)_Export_ALAC.png (25.22 KiB) Viewed 997 times

Here's the stats on the EXT PROG file:

FTIC_(22 kHz)_Export_ALAC_M4A.png (12.72 KiB) Viewed 997 times

So the question is: which file is compressed LOSSLESS and which one is LOSSY?

Also.. he says he exports his audio in Mac GarageBand to an MP4 container? Is that correct?


-Ed

[edwinn]

Gotta' compliment you developer guys on the Export feature of v2.2.1

I'm an old RazorLame and FLAC Frontend user.. and used to hang out at Hydrogen Audio.

http://www.dors.de/razorlame/screenshots.php

http://flacfrontend.sourceforge.net/


Great export dialog boxes and Audacity HELP files!


-Ed

[steve]

So the question is: which file is compressed LOSSLESS and which one is LOSSY?

Both are lossy.

If you want lossless, I'd recommend sticking with 16-bit WAV (compatible with everything), 24-bit WAV (all studios should be able to support this, but 50% bigger than 16-bit, and rather over the top for speech recording), or FLAC (half the size of WAV and much better metadata support).
If you really want ALAC, you could try Foobar2000 to convert from WAV.

Note that these days, a $10 memory stick can hold many hours of uncompressed mono WAV files.

[edwinn]

Thanks for the reply.

Isn't ALAC supposed to be lossless? like FLAC? What am I missing? Is there no lossless Apple format?

See definition here > > https://en.wikipedia.org/wiki/Apple_Lossless


The Mac user guy says the container is MP4, which sounded lossy to me.

BTW, the 1624k file I exported to M4A using `External Program´ command line is equivalent to the 1632k file exported in FLAC as follows:

file_sizes.png (3.92 KiB) Viewed 988 times

So I assumed they were both lossless compressed, and don't want to mis-advise the Mac user guy.

Maybe need to come up with a verification test of some kind?


-Ed

[DVDdoug]

So the question is: which file is compressed LOSSLESS and which one is LOSSY?

I've never used ALAC or GarageBand, but I'd say the 243kbps file is probably lossless.

MediaInfo might tell you for sure.

A "regular" 16-bit 44.1kHz stereo FLAC or ALAC is usually in the ballpark of 700kbps. At 22kHz, you've got half the data, and I assume your file is mono. (22.050kHz, 16-bit mono uncompressed is 352kbps.)

Although it's a good idea to record & produce in a lossless format it's more practical to distribute in a more-compressed format. You are not likely to hear any difference, especially with a spoken word, which I assume is recorded under non-ideal conditions in a "noisy" lecture hall.

BTW - If you are going to use lossless, you might as well record at 44.1 or 48kHz. Your lossless files will be larger, but you don't have to distribute those original files.

Isn't ALAC supposed to be lossless? like FLAC? What am I missing? Is there no lossless Apple format?

Yes, ALAC is lossless. I don't know if your AAC file is ALAC.

, which sounded lossy to me.

What does that mean? Sounded lossy compared to what?

[steve]

Both are lossy.

I've re-read your post and I've changed my mind.
Initially I was just looking at the bit-rate, (243 kbps) which is too low for stereo music.

Looking at your ffmpeg settings, that should be correct for ALAC lossless, and I presume that you were exporting a mono track.

[steve]

Maybe need to come up with a verification test of some kind?

With the original track still in Audacity, import the M4A file.
Apply the "Invert" effect to the M4A track.
Select both tracks and "Tracks menu > Mix > Mix and Render".

The result should be absolute silence if both tracks were identical (the inverted copy is the exact equal and opposite of the original).

To test for "absolute" silence:
Select the track and open the Amplify effect. The Amplify effect should say the the "New peak amplitude" will be "-Infinity".

Note that if the original track is greater than 16-bit precision, this test will not give "absolute" silence (due to rounding of the sample values). It will give extremely low level hiss at around -90 dB

[edwinn]

Both are lossy.

I've re-read your post and I've changed my mind.
Initially I was just looking at the bit-rate, (243 kbps) which is too low for stereo music.

Looking at your ffmpeg settings, that should be correct for ALAC lossless, and I presume that you were exporting a mono track.

Yes.. it's a 22 kHz mono track.

Thanks


-Ed

[edwinn]

Maybe need to come up with a verification test of some kind?

With the original track still in Audacity, import the M4A file.
Apply the "Invert" effect to the M4A track.
Select both tracks and "Tracks menu > Mix > Mix and Render".

The result should be absolute silence if both tracks were identical..

Thanks, great idea. Learning new tricks here.

-Ed

[edwinn]

So the question is: which file is compressed LOSSLESS and which one is LOSSY?

I've never used ALAC or GarageBand, but I'd say the 243kbps file is probably lossless.

MediaInfo might tell you for sure.

A "regular" 16-bit 44.1kHz stereo FLAC or ALAC is usually in the ballpark of 700kbps.
At 22kHz, you've got half the data, and I assume your file is mono. (22.050kHz, 16-bit mono uncompressed is 352kbps.)

ALAC is lossless. I don't know if your AAC file is ALAC.

, which sounded lossy to me.

What does that mean? Sounded lossy compared to what?

Haven't seen a screen-cap of the guy's GarageBand app.. but see the following:

https://www.apple.com/mac/garageband/


MediaInfo was VERY helpful!!

MediaInfo.png (5.18 KiB) Viewed 982 times

Does AAC LC in table above mean 'lossy compression"?


"sounds lossy to me" means.. intuitively Mpeg sounded like a lossy codec, however MediaInfo (above) shows `MPEG-4 Lossless´.

Please comment more.


-Ed