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Can I "extract" 1 channel from a stereo mp3?

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Anonymous
September 15, 2005 1:01:28 AM

Archived from groups: rec.audio.pro (More info?)

I have many mp3's of talk radio shows which were recorded as stereo mp3
files. The audio content is really the same on both channels, so the
encoding is very inefficient. These files are twice the data size that
they could have been if they had been originally recorded as mono
files. The mp3's are the only source available, so I can't go back to
a higher quality source.

I have been looking around for weeks to find an mp3 converter than can
"extract" one of the channels from a stereo mp3 file. I want to make
new mono files with the same sound quality but half the data size. I
really don't want to re-encode or re-sample anything! So far I have
had no luck finding what I need. Is it possible to do this?

Thanks, R2
Anonymous
September 15, 2005 8:57:28 AM

Archived from groups: rec.audio.pro (More info?)

<r2mhf@yahoo.com> wrote in message
news:1126753909.154951.42930@z14g2000cwz.googlegroups.com
> I have many mp3's of talk radio shows which were recorded
> as stereo mp3 files. The audio content is really the
> same on both channels, so the encoding is very
> inefficient. These files are twice the data size that
> they could have been if they had been originally recorded
> as mono files. The mp3's are the only source available,
> so I can't go back to a higher quality source.
>
> I have been looking around for weeks to find an mp3
> converter than can "extract" one of the channels from a
> stereo mp3 file. I want to make new mono files with the
> same sound quality but half the data size. I really
> don't want to re-encode or re-sample anything! So far I
> have had no luck finding what I need. Is it possible to
> do this?

Your point seems to be well-taken, but I don't know how much
waste there really is if the recordings are done in joint
stereo.
Anonymous
September 15, 2005 9:11:28 AM

Archived from groups: rec.audio.pro (More info?)

On 9/15/05 12:01 AM, in article
1126753909.154951.42930@z14g2000cwz.googlegroups.com, "r2mhf@yahoo.com"
<r2mhf@yahoo.com> wrote:

> I have many mp3's of talk radio shows which were recorded as stereo mp3
> files. The audio content is really the same on both channels, so the
> encoding is very inefficient. These files are twice the data size that
> they could have been if they had been originally recorded as mono
> files. The mp3's are the only source available, so I can't go back to
> a higher quality source.
>
> I have been looking around for weeks to find an mp3 converter than can
> "extract" one of the channels from a stereo mp3 file. I want to make
> new mono files with the same sound quality but half the data size. I
> really don't want to re-encode or re-sample anything! So far I have
> had no luck finding what I need. Is it possible to do this?
>
> Thanks, R2
>
Don;t you just re-construct the file as a MONO mp3?
Related resources
September 16, 2005 8:37:57 PM

Archived from groups: rec.audio.pro (More info?)

The files are twice as big as they need to be. That means the amount
of wasted data is 50% of the total. That is A LOT of wasted space as
far as I am concerned. Don't you agree?

The only way I know how to "reconstruct" a file as mono is to
"re-sample" or "re-encode" it. As I said, I don't want to lose sound
quality through the re-sampling process.

I am a bit disapointed that no one seems to know the answer to my
question, so please let me state the question again. Is it possible to
extract one channel into a mono mp3 file without losing any sound
quality?

Thanks, R2
September 16, 2005 9:39:31 PM

Archived from groups: rec.audio.pro (More info?)

Well I would also like to hear back from Arny on this one. But to be
sure just took a CD quality audio file of 2:35 and 26MB. I turned it
into a stereo 128 kpbs file of 2.36MB and also a corresponding mono
file at 64 kbps containing 1.18MB. The actual bit rate per channel is
the same but the file is exactly one half the size. Am I missing
something here or is it not true that mono mp3 files are exactly one
half the size of a stereo mp3 at the same bit rate?
September 16, 2005 9:57:19 PM

Archived from groups: rec.audio.pro (More info?)

I fully understand what you are saying about LOSSY compression. That
is exactly why I was hoping for a way to extract a channel without
re-sampling it. The original file sounds OK. I just don't want to
cause any more loss.
Anonymous
September 17, 2005 2:04:30 AM

Archived from groups: rec.audio.pro (More info?)

R2 <r2mhf@yahoo.com> wrote:
>I fully understand what you are saying about LOSSY compression. That
>is exactly why I was hoping for a way to extract a channel without
>re-sampling it. The original file sounds OK. I just don't want to
>cause any more loss.

What you are missing is that the lossy compression scheme basically
throws away information that isn't important... and if both channels
are the same and the encoder is set up for coupled stereo, it will
not bother storing any L-R stereo information in the file because
there will be nothing to store.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
September 17, 2005 4:18:40 AM

Archived from groups: rec.audio.pro (More info?)

On 16 Sep 2005 16:37:57 -0700, "R2" <r2mhf@yahoo.com> wrote:

>The files are twice as big as they need to be. That means the amount
>of wasted data is 50% of the total. That is A LOT of wasted space as
>far as I am concerned. Don't you agree?

Arny can speak for himself, but part of his point
is that your 50% assumption is incorrect for MP3's.

Good fortune,

Chris Hornbeck
Irony and sarcasm emoticons available by request.
You place 'em.
Anonymous
September 17, 2005 4:42:11 AM

Archived from groups: rec.audio.pro (More info?)

On 9/16/05 7:37 PM, in article
1126913877.573747.274170@z14g2000cwz.googlegroups.com, "R2"
<r2mhf@yahoo.com> wrote:

> The files are twice as big as they need to be. That means the amount
> of wasted data is 50% of the total. That is A LOT of wasted space as
> far as I am concerned. Don't you agree?
>
> The only way I know how to "reconstruct" a file as mono is to
> "re-sample" or "re-encode" it. As I said, I don't want to lose sound
> quality through the re-sampling process.
>
> I am a bit disapointed that no one seems to know the answer to my
> question, so please let me state the question again. Is it possible to
> extract one channel into a mono mp3 file without losing any sound
> quality?

Look, you;re ALREADY into lossy compression here. Without access to the
original file, the best you can do is a real clean re-compress-to-mono.
I don;t know if there's anything better than that. The damage has been done.
Just use a GOOD encoder to do the new process.
Anonymous
September 17, 2005 5:04:42 AM

Archived from groups: rec.audio.pro (More info?)

On 16 Sep 2005 17:39:31 -0700, "R2" <r2mhf@yahoo.com> wrote:

>Well I would also like to hear back from Arny on this one. But to be
>sure just took a CD quality audio file of 2:35 and 26MB. I turned it
>into a stereo 128 kpbs file of 2.36MB and also a corresponding mono
>file at 64 kbps containing 1.18MB. The actual bit rate per channel is
>the same but the file is exactly one half the size. Am I missing
>something here or is it not true that mono mp3 files are exactly one
>half the size of a stereo mp3 at the same bit rate?

Do a google search on "joint stereo" + "MP3" or some such
on this newsgroup, and you'll get some appropriate info.
It's arisen fairly recently.

Sorry, it's not a topic I'm personally interested in, so
can't quote authoritatively. The gist is that some (all?)
MP3 encoders operate on the sum and difference separately,
with different audibility weightings. I damn sure would, if I
had to design one.

Good fortune,

Chris Hornbeck
Irony and sarcasm emoticons available by request.
You place 'em.
Anonymous
September 17, 2005 5:16:02 AM

Archived from groups: rec.audio.pro (More info?)

On 16 Sep 2005 17:57:19 -0700, "R2" <r2mhf@yahoo.com> wrote:

>I fully understand what you are saying about LOSSY compression. That
>is exactly why I was hoping for a way to extract a channel without
>re-sampling it. The original file sounds OK. I just don't want to
>cause any more loss.

I guess it's just a sign of the national emotional
numbness in the wake of the disater that you haven't
received a half dozen posts to the effect of:

"Then leave it the hell alone. It's already an MP3,
fercrissakes" complete with exclamation marks.

But nobody has the energy. Lucky you,

Chris Hornbeck
Irony and sarcasm emoticons available by request.
You place 'em.
Anonymous
September 17, 2005 6:49:42 AM

Archived from groups: rec.audio.pro (More info?)

On 9/16/05 8:39 PM, in article
1126917570.954447.117670@f14g2000cwb.googlegroups.com, "R2"
<r2mhf@yahoo.com> wrote:

> Well I would also like to hear back from Arny on this one. But to be
> sure just took a CD quality audio file of 2:35 and 26MB. I turned it
> into a stereo 128 kpbs file of 2.36MB and also a corresponding mono
> file at 64 kbps containing 1.18MB. The actual bit rate per channel is
> the same but the file is exactly one half the size. Am I missing
> something here or is it not true that mono mp3 files are exactly one
> half the size of a stereo mp3 at the same bit rate?
>

Rememeber, the COMPRESSED DATA FILE is NOT a real representation of the
resultant listenable music file.

Now I have NO idea how these thigns work, but going on the idea that if -I-
can think of a half-clever way to solve this problem, the real
number-cruncher and statistical-analysis guys must've already come up with a
WAYYYYY more effective and efficient approach...
With that in mind:
Considering how smart the compression program at hand might be, it depends
on the music at any moment and how much DIFFERENCE there actually is in the
mix L vs R. Much music is pretty darned mono (especially in the bass) in
general and a good program may well not actually use up anything NEAR
twice-as-much storage for a stereo-vs-mono version...

I could see it looking at the mix NOT as LEFT-ch and RIGHT-ch,
but as a
L+R channel
and a
L-R channel...
And if the stereo info was minimal, the L-R channel wouldn't have all that
much data over what's already in the L+R channel... The STEREO encoded file
might only have, say 10% more data in the file than the MONO version.

In your case, with LEFT being the SAME as RIGHT, there would be the data
amount from whatever it did dealing with the L+R channel,
and then, since there would be NOTHING in the L-R channel, your resultant
data file would be pretty much identical for a mono or a stereo version.
For all you know, you already HAVE it as far down as it can go.
Anonymous
September 17, 2005 7:19:49 AM

Archived from groups: rec.audio.pro (More info?)

R2 wrote:
> The files are twice as big as they need to be. That means the amount
> of wasted data is 50% of the total. That is A LOT of wasted space as
> far as I am concerned. Don't you agree?
>
> The only way I know how to "reconstruct" a file as mono is to
> "re-sample" or "re-encode" it. As I said, I don't want to lose sound
> quality through the re-sampling process.
>
> I am a bit disapointed that no one seems to know the answer to my
> question, so please let me state the question again. Is it possible to
> extract one channel into a mono mp3 file without losing any sound
> quality?
>
> Thanks, R2
>

Convert it to stereo .wav, open it in an audio editor such as Cubase or
PT that will allow you to split the .wav into two seperate mono
channels, then export one, or both of the channels to a mono .wav or
..mp3....a lot of radio mixes are either done in mono, or mixed in such a
way that it doesn't entirely matter what channel you take....pick, L, or
R, or both, export it, and you'll be fine........Best of luck!

Jonny Durango
Anonymous
September 17, 2005 9:26:31 AM

Archived from groups: rec.audio.pro (More info?)

R2 wrote:
> I fully understand what you are saying about LOSSY compression. That
> is exactly why I was hoping for a way to extract a channel without
> re-sampling it. The original file sounds OK. I just don't want to
> cause any more loss.

The least intrusive thing you can do is play it back through the best
(analog) player you have, and re-record it through the best (analog)
recorder you have. I suppose you could call the "re-sampling" but it's
a real process, not a mathematical one. With today's equipment, even
inexpensive equipment, while the result may not be mathematically
equivalent to the source, it isn't going to sound enough different to
matter.

Screw programs. Just use a cable. In less that the time it takes to
find the perfect program, download and install it, figure out how to
work it, and do the job, you could be listening to your half-sized
recording in glorious mono.
Anonymous
September 17, 2005 1:12:25 PM

Archived from groups: rec.audio.pro (More info?)

R2 wrote:

> Am I missing something here or is it not true that mono mp3 files are
exactly one
> half the size of a stereo mp3 at the same bit rate?

What you are missing is that the majority of mp3 stereo encodings at
128k or less are done using "joint stereo", a technique that takes
advantage of the fact that the left and right channels of a stereo music
signal are very similar. Joint stereo gives far better sound for a given
bit rate than encoding the two channels independently at half the bit
rate each.

So it's likely that your 128k stereo MP3 is joint stereo. if you convert
to mono at 64k, you will get half the file size all right, but you'll
get a drop in sound quality. You'd need to re-encode at about 96k to
keep equivalent quality, resulting in a file size reduction of only 25%,
for example.

By the way, the LAME encoder <http://lame.sf.net&gt; will take an MP3 as
input, for re-ecoding in a different format. That what I use; I can't
speak for other software.

--
Anahata
anahata@treewind.co.uk -+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827
Anonymous
September 17, 2005 3:48:27 PM

Archived from groups: rec.audio.pro (More info?)

"R2" <r2mhf@yahoo.com> wrote in message
news:1126913877.573747.274170@z14g2000cwz.googlegroups.com

> The files are twice as big as they need to be. That
> means the amount of wasted data is 50% of the total.
> That is A LOT of wasted space as far as I am concerned.
> Don't you agree?


I don't know if I agree or disagree because I don't know all
the facts.

For example, if the file is coded in joint stereo mode, the
bandwidth that is allocated to the L+R data is usually far
greater than the bandwidth allocated to the L-R data. This
can work because there may not be a lot of useful
information in the L-R domain. IOW, you have a single person
speaking close to a microphone and/or in a dead space, so
the information is essentially mono.

What you are suggesting is do away with the L-R channel
which makes a lot of sense for a single person speaking.

But, if your MP3 coder is already allocating most of the
available bandwidth to the L+R data, then downconverting to
mono won't save a lot of bandwidth.


> The only way I know how to "reconstruct" a file as mono
> is to "re-sample" or "re-encode" it. As I said, I don't
> want to lose sound quality through the re-sampling
> process.

Yes, transcodeing MP3 is far from a slam dunk.

> I am a bit disapointed that no one seems to know the
> answer to my question, so please let me state the
> question again. Is it possible to extract one channel
> into a mono mp3 file without losing any sound quality?

Not necessarily. Some MP3 coders are *smart* enough to
figure out that the audio is essentially mono, and code it
accordingly.
September 18, 2005 4:47:19 PM

Archived from groups: rec.audio.pro (More info?)

Thanks for all the input. I now have a few ideas about where to go
with this. But for now I will probably just keep the files as they
are.

I knew that mp3 encoding was complicated but I found out that it was
even more complicated than I thought.

R2
Anonymous
September 19, 2005 2:08:05 PM

Archived from groups: rec.audio.pro (More info?)

"R2" <r2mhf@yahoo.com> wrote in message
news:1127072839.042093.305570@f14g2000cwb.googlegroups.com
> Thanks for all the input. I now have a few ideas about
> where to go with this. But for now I will probably just
> keep the files as they are.
>
> I knew that mp3 encoding was complicated but I found out
> that it was even more complicated than I thought.


Huzzah! That was the message that several of us were trying
to communicate.

Enjoy!
Anonymous
September 20, 2005 4:46:07 PM

Archived from groups: rec.audio.pro (More info?)

On 14 Sep 2005 21:01:28 -0700, r2mhf@yahoo.com wrote:

>I have been looking around for weeks to find an mp3 converter than can
>"extract" one of the channels from a stereo mp3 file. I want to make
>new mono files with the same sound quality but half the data size. I
>really don't want to re-encode or re-sample anything! So far I have
>had no luck finding what I need. Is it possible to do this?

The process you describe is called "Re-encoding as a mono MP3". If
you are dead set against re-encoding, you're going to find it
difficult :-)

Open the MP3 in an audio editor. Save As, choosing appropriate MP3
settings.
Anonymous
September 20, 2005 4:48:46 PM

Archived from groups: rec.audio.pro (More info?)

On 16 Sep 2005 16:37:57 -0700, "R2" <r2mhf@yahoo.com> wrote:

>I am a bit disapointed that no one seems to know the answer to my
>question, so please let me state the question again. Is it possible to
>extract one channel into a mono mp3 file without losing any sound
>quality?

If you re-encode at the same bit-rate you'll lose very little if any
quality. It's only a MP3 for goodness' sake! If you'd wanted
quality you'd have recorded a wav.
Anonymous
September 20, 2005 4:49:49 PM

Archived from groups: rec.audio.pro (More info?)

On 16 Sep 2005 17:57:19 -0700, "R2" <r2mhf@yahoo.com> wrote:

>I fully understand what you are saying about LOSSY compression. That
>is exactly why I was hoping for a way to extract a channel without
>re-sampling it. The original file sounds OK. I just don't want to
>cause any more loss.

Have you tried? I think you'll discover your fears are unfounded.
Anonymous
September 20, 2005 4:50:27 PM

Archived from groups: rec.audio.pro (More info?)

On Sat, 17 Sep 2005 01:16:02 GMT, Chris Hornbeck
<chrishornbeckremovethis@att.net> wrote:

>I guess it's just a sign of the national emotional
>numbness in the wake of the disater that you haven't
>received a half dozen posts to the effect of:

What nation? :-)
Anonymous
September 20, 2005 4:51:47 PM

Archived from groups: rec.audio.pro (More info?)

On 16 Sep 2005 22:04:30 -0400, kludge@panix.com (Scott Dorsey) wrote:

>What you are missing is that the lossy compression scheme basically
>throws away information that isn't important... and if both channels
>are the same and the encoder is set up for coupled stereo, it will
>not bother storing any L-R stereo information in the file because
>there will be nothing to store.

Does MP3 compression analyse for stereo content before compressing?
Which encoder are you using?
Anonymous
September 20, 2005 4:56:01 PM

Archived from groups: rec.audio.pro (More info?)

On 18 Sep 2005 12:47:19 -0700, "R2" <r2mhf@yahoo.com> wrote:

>Thanks for all the input. I now have a few ideas about where to go
>with this. But for now I will probably just keep the files as they
>are.
>
>I knew that mp3 encoding was complicated but I found out that it was
>even more complicated than I thought.

Except that, for your application regarding a mono speech broadcast,it
really isn't complicated at all. Just do it. You started out with
adequate, but not wonderful quality. You'll end up with the same.

If this was a quality music recording we'd first be slamming you for
going anywhere near MP3 in the first place, then suggesting ways of
minimising further damage. But speech is very undemanding.
Anonymous
September 20, 2005 5:14:14 PM

Archived from groups: rec.audio.pro (More info?)

Laurence Payne wrote:
> Does MP3 compression analyse for stereo content before compressing?

It does what you ask it to!

If the input is stereo, MP3 compression can do one of three things,
usually all selectable by the user:
(1) make a mono mp3 file by encoding L+R
(2) make a true stereo MP3 by encoding L and R independently
(3) Joint stereo, which capitalizes on the inherent redundancy of stereo
audio, i.e. the L and R channels have similar content.

The "Lame" encoder by default selects joint stereo for any bit rate
below some threshold (160k I think) and normal stereo otherwise.

Anahata
September 21, 2005 1:55:53 AM

Archived from groups: rec.audio.pro (More info?)

Just for the record I have tried using both Cool Edit and Adobe
Audition on this task. Both of them automatically convert an mp3 to
wav when you load the file. Therefore the only way to edit an mp3 is
to convert to wav and back to mp3. I could find no way of changing
this setting. I can't really complain about that though, both are sold
was wav editors and not mp3 editors.

R2
Anonymous
September 21, 2005 6:01:27 AM

Archived from groups: rec.audio.pro (More info?)

"R2" <r2mhf@
> I am a bit disapointed that no one seems to know the answer to my
> question, so please let me state the question again. Is it possible to
> extract one channel into a mono mp3 file without losing any sound
> quality?
>
In Cool Edit/Adobe Audition you can load a stereo file and select
Edit>Edit Channel>(Left/Right) Channel. After that, Copy and Paste to a New
file.

Job done, One channel of your original stereo, as a seperate Mono track.

What software do you have? I've not followed this one closely as I can't
remember the details.

Rv!
Anonymous
September 21, 2005 6:52:43 AM

Archived from groups: rec.audio.pro (More info?)

R2 wrote:
> Just for the record I have tried using both Cool Edit and Adobe
> Audition on this task. Both of them automatically convert an mp3 to
> wav when you load the file. Therefore the only way to edit an mp3 is
> to convert to wav and back to mp3. I could find no way of changing
> this setting.

Probably because there isn't any better way of doing it. :-)


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
Anonymous
September 21, 2005 9:05:01 AM

Archived from groups: rec.audio.pro (More info?)

On 20 Sep 2005 21:55:53 -0700, "R2" <r2mhf@yahoo.com> wrote:

>Just for the record I have tried using both Cool Edit and Adobe
>Audition on this task. Both of them automatically convert an mp3 to
>wav when you load the file. Therefore the only way to edit an mp3 is
>to convert to wav and back to mp3. I could find no way of changing
>this setting. I can't really complain about that though, both are sold
>was wav editors and not mp3 editors.

You may be interested in the editors on mp3fe.com .

Their freeware .mp3 to .wav convertor works better than
most although it balks at flakey sources. (The temp
file it leaves is still often usable.)

Good fortune,

Chris Hornbeck
Anonymous
September 27, 2005 5:03:28 PM

Archived from groups: rec.audio.pro (More info?)

On 20 Sep 2005 21:55:53 -0700, "R2" <r2mhf@yahoo.com> wrote:

>Just for the record I have tried using both Cool Edit and Adobe
>Audition on this task. Both of them automatically convert an mp3 to
>wav when you load the file. Therefore the only way to edit an mp3 is
>to convert to wav and back to mp3. I could find no way of changing
>this setting. I can't really complain about that though, both are sold
>was wav editors and not mp3 editors.

ARE there editors that work directly on MP3 files, for any process
beyond a bit of simple cutting and splicing perhaps? It's like
asking Word to work on a file in a ZIP archive without extracting it.
The extraction and re-compression may be transparent to the user, but
it still has to happen.
Anonymous
September 27, 2005 6:28:24 PM

Archived from groups: rec.audio.pro (More info?)

Laurence Payne wrote:
>
> ARE there editors that work directly on MP3 files, for any process
> beyond a bit of simple cutting and splicing perhaps?

I believe it's possible to change the volume level of an MP3 by editing
a scale factor that's part of each encoding block, with some
limitations, and there are numerous utilities for editing ID tags.

As far as I know, anything else requires decoding and re-encoding.

Anahata
!