IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
How to convert 2-channel mono m4a tracks to 1-channel without reencodi
Wally Walters
post Feb 16 2012, 18:56
Post #1





Group: Members
Posts: 19
Joined: 16-April 07
Member No.: 42587



The title pretty much says it all. I have several mono songs that were encoded into 2-channel .m4a tracks by the Nero encoder, and would like to strip out one of the two identical channels without reencoding. How would I go about this? Thanks.
Go to the top of the page
+Quote Post
pdq
post Feb 16 2012, 19:11
Post #2





Group: Members
Posts: 3374
Joined: 1-September 05
From: SE Pennsylvania
Member No.: 24233



If your goal is to make the files smaller then you will probably be disappointed. Mono files encoded as stereo typically are about the same size as if they were encoded mono.

Edit: assuming vbr (quality based) encoding.

This post has been edited by pdq: Feb 16 2012, 19:13
Go to the top of the page
+Quote Post
saratoga
post Feb 16 2012, 19:38
Post #3





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



QUOTE (Wally Walters @ Feb 16 2012, 12:56) *
I have several mono songs that were encoded into 2-channel .m4a tracks by the Nero encoder, and would like to strip out one of the two identical channels without reencoding.


Except in special circumstances, this isn't possible because of how M/S coding works in AAC. Just leave them as stereo.
Go to the top of the page
+Quote Post
Wally Walters
post Feb 16 2012, 19:45
Post #4





Group: Members
Posts: 19
Joined: 16-April 07
Member No.: 42587



QUOTE (pdq @ Feb 16 2012, 12:11) *
If your goal is to make the files smaller then you will probably be disappointed. Mono files encoded as stereo typically are about the same size as if they were encoded mono.

Edit: assuming vbr (quality based) encoding.


Fascinating. Slightly off the subject, does that mean a mono CD rip can be encoded to m4a in either mono or stereo at the same bitrate, with equivalent results?
Go to the top of the page
+Quote Post
saratoga
post Feb 16 2012, 20:08
Post #5





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



QUOTE (Wally Walters @ Feb 16 2012, 13:45) *
Slightly off the subject, does that mean a mono CD rip can be encoded to m4a in either mono or stereo at the same bitrate, with equivalent results?


Assuming the encoder is intelligent, you'll get fairly similar results.
Go to the top of the page
+Quote Post
DVDdoug
post Feb 16 2012, 20:58
Post #6





Group: Members
Posts: 2537
Joined: 24-August 07
From: Silicon Valley
Member No.: 46454



QUOTE
Fascinating. Slightly off the subject, does that mean a mono CD rip can be encoded to m4a in either mono or stereo at the same bitrate, with equivalent results?
M/S encoding works by taking the L & R channels and creating a L+R channel (mid) and a L-R (side) channel. (This process is 100% reversable, without loss.)

With a regular stereo recording, there is a lot of "center channel" sound that's common to both channels. So after M/S encoding, there is more in formation in the L+R channel than the L-R channel, and the stuff that's the same in both channels doesn't have to be encoded twice.

If you have a dual-mono recording (with the same information in both channels), the L-R channel contains silence and the lossy encoder knows not to waste space encoding silence.

If you have a stereo file with nothing in common between the channels, say English dialog in the left, and French dialog in the right, then there is no advantage, but very little harm either. (In this case, LAME would not use M/S when encoding MP3s in Joint Stereo, and I'm assume the AAC encoder is just as smart.)


Note that with uncompressed audio, there is no space-saving with M/S because it takes just as much space to hold 16-bits of silence as it does to hold 16-bits of actual audio. In fact, when you add/subtract two 16-bit numbers, it can take 17-bits to hold the result (depending on the value and +/- sign of the numbers being added/subtracted). Somewhere in the audio file there will be results that don't fit into 16-bits, so it actually takes up more space...
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 - 13:12