Cut MB from 36 to under 25 to enable email

[whomper]

maybe
but my isp does not allow it
i either use their web interface
or i take it all shoved into my inbox whenever i check the mail
and that includes all attachments whether i want them or not

that is the one thing better about hotmail
*I* can choose whether to dl or not

[kozikowski]

<<<When exporting in a lossy compressed format, the bit rate (and hence the file size) remains the same irrespective of the number of audio channels>>>

True, but the quality goes up and down. Mono at 64 works much better than Stereo at 64.

Koz

[ignatz]

... If you export that show, the filesize should be almost exactly half...

Only when exporting in an uncompressed format. When exporting in a lossy compressed format, the bit rate (and hence the file size) remains the same irrespective of the number of audio channels (see here: http://forum.audacityteam.org/viewtopic ... 194#p93189 )

Steve:

Could you expound on the above? I read the link you gave and am still unclear.

I just did some tests.

Source Mp3 1: joint stereo, bitrate 186; 3.68 MB; opened it in Audacity, did a stereo track to mono, and exported.

Resulting file is 2.06 MB, mono, 104 bitrate

Source Mp3 2: joint stereo, bitrate 192; 5.37 MB; opened it in Audacity, did a stereo track to mono, and exported.

Resulting file is 3.15 MB, mono, 112 bitrate

Source Mp3 3: stereo recording of mono original; bitrate 192; 4.72 MB; opened it in Audacity, did a stereo track to mono, and exported.

Resulting file is 2.53 MB, mono, 103 bitrate

If it matters, my file export options for mp3s are set to variable, quality 2 170-210 kbps, fast speed and joint stereo.

I'm obviously misunderstanding your comment--the files sizes in my tests were both reduced by roughly 40%. You apparently meant something else, but I'm not sure what.

The bitrate information is as obtained from Encspot.

[steve]

When you import a compressed audio file into Audacity, it is decoded into uncompressed audio data.
When you export from Audacity to a compressed format (such as MP3), it is the (uncompressed) audio data within the Audacity project that is encoded, not the original MP3 file.

In that sense it is irrelevant what the format of the source file is because Audacity is not encoding the source file, it is encoding the uncompressed data within the project.
The test you should be doing to verify the difference between mono encoding and stereo encoding is not comparing the output file to the input file, but comparing a mono output file to a stereo output file.

When using VBR (Variable Bit Rate) encoding, Lame aims to produce audio at the set "Quality". The actual data rate may vary, but as a rough guide is expected to be within the range indicated. For example "Standard Quality" is expected to be somewhere in the range 170-210 kbps. The actual data rate depends not only on the "Quality" setting, but on the complexity of the audio that is being encoded. This is the big advantage of VBR encoding - it uses a higher bit rate for complex sound (where a higher bit rate is needed) and a lower bit rate for less complex sounds (where it is less critical).

Using Lame 3.98 in Audacity (not all encoders use the same strategy):
If you encode a mono file with VBR, the encoder will use more "bits per second" for a stereo file than it will for a mono file, because there is more information to encode (the stereo file is more complex). Thus a stereo VBR file will have a higher bit-rate and a larger file size than a mono track. VBR encoding aims to produce sound of a set quality, and adjusts the bit-rate as required.

When recording with constant bit rate (CBR) or average bit rate (ABR), the "target" that Lame aims for is the "bit rate".

In the case of CBR, the bit rate will be as set (for example 128 kbps) irrespective of the complexity or number of channels in the source audio (the "source audio" being the uncompressed data within the Audacity project).

In the case of ABR, the bit rate will be adjusted according to the complexity, but will aim to be close to the set bit rate. So whether a mono or stereo source, whether simple or complex, a setting of (say) 160 kbps ABR will have an average bit rate that is close to 160 kbps. Thus the file size will be roughly the same whether it is mono or stereo.

[ignatz]

The test you should be doing to verify the difference between mono encoding and stereo encoding is not comparing the output file to the input file, but comparing a mono output file to a stereo output file.

Steve:

I just did another test comparing mono output to stereo output as you advise above:

Source mp3: joint stereo; 3,863,021 bytes, bit rate 186

Mono mp3 export: 2,166,806 bytes; bit rate 104

Stereo mp3 export: 4,333,847; bit rate 209


You had stated earlier:

"When exporting in a lossy compressed format, the bit rate (and hence the file size) remains the same irrespective of the number of audio channels".

So, my confusion continues. Neither the bit rate nor the file size "remains the same irrespective of the number of audio channels" (104 versus 209 bit rates and 2,166,806 versus 4.333,847 file sizes) when comparing mono exports to stereo exports.

What am I missing here?

What test can I conduct on my end to verify that ""When exporting in a lossy compressed format, the bit rate (and hence the file size) remains the same irrespective of the number of audio channels"?

[kozikowski]

Sometimes Audacity "helps you out" in the background leading to oddball, unpredictable results.

I loaded my stereo piano solo into Audacity and exported a 128 bitrate MP3. 100KB.
Tracks > Stereo Track to mono. Export MP3. 100KB.

If I export non-compressed WAV files, the two files are 1200KB and 592KB. Half and double.

Koz

[kozikowski]

And just to bring this around, the quality of the two uncompressed wav files is constant -- good to excellent.

The musical quality of the mono MP3 is double that of the stereo MP3. The quality goes up and down with the bitrate and reverse with the number of channels. You really have to know what you're doing with music data compressors. The presentation quality can change with some odd conditions and tools. Compressors are Front Loaded. The more work and time and care you take at the compression step, the higher the quality when the client listens to it -- at the same bitrate.

Koz

[steve]

So, my confusion continues. Neither the bit rate nor the file size "remains the same irrespective of the number of audio channels" (104 versus 209 bit rates and 2,166,806 versus 4.333,847 file sizes) when comparing mono exports to stereo exports.

What am I missing here?

VBR vs CBR vs ABR.

I failed to differentiate between these in my original post.
As I've tried to clarify in my last post, my original statement applies to CBR and ABR but not VBR.

In older versions of Audacity VBR was not available, so it was previously the case that mono or stereo files would always produce files of similar size. In Audacity 1.3.12 VBR is available, and with VBR the bit rate and file size for mono tracks will be around half of that for an equivalent stereo track. Apologies if I caused confusion, but hopefully it's clear now?

[ignatz]

In older versions of Audacity VBR was not available, so it was previously the case that mono or stereo files would always produce files of similar size. In Audacity 1.3.12 VBR is available, and with VBR the bit rate and file size for mono tracks will be around half of that for an equivalent stereo track. Apologies if I caused confusion, but hopefully it's clear now?

Tentatively clear, at least.

I upgraded to 1.3.12 only a couple of days ago, so can't verify any behavior on earlier versions. The tests I have made were done with 1.3.12.

I have 2 main concerns:

1: the possible negative effects of using "stereo to mono" when the source mp3 is 2 channel mono (IE; a 2 channel mp3 of a pre-stereo era recording).

From your prior comments, I assume the chance of a negative effect is virtually zero--one instance in your entire experience.


2: Possible negative effects of opening an mp3, modifying it (stereo to mono, denoise, whatever) and then exporting as mp3 again.

I have it in my head that it is bad form to open and re-export an mp3 file repeatedly because a little more data is thrown out (forever and irretrievably) on each new export. Having said that, I have opened and exported certain mp3s multiple times with no noticeable effect as yet. Is it not bad form? Or I could have tin ears?

Maybe the answer is in this earlier quote from you. Maybe it isn't bad form?

"When you import a compressed audio file into Audacity, it is decoded into uncompressed audio data.
When you export from Audacity to a compressed format (such as MP3), it is the (uncompressed) audio data within the Audacity project that is encoded, not the original MP3 file.

In that sense it is irrelevant what the format of the source file is because Audacity is not encoding the source file, it is encoding the uncompressed data within the project."

Being an amateur, I don't entirely follow that.

I am just concerned with causing audible degradation by repeated opening and exports of the same mp3. I'm not sure what the quote immediately above means for my purposes.

I'm contemplating doing a mass stereo to mono conversion of thousands of 2 channel mono era recordings, but that would entail a new export as mp3, so the bad form issue arises.

The only time I use WAV files is when I am compiling just a few tracks for a CD. Otherwise, I am mp3 (VBR) all the way, with playback from PC through a home stereo system.

Comments?

[kozikowski]

<<<Is it not bad form? Or I could have tin ears?>>>

It's bad form, but might not be terrible. Everything in compressed audio (and video) depends on everything else.

If you import a top quality MP3 file (almost impossible, but work with me here) then Audacity will convert it to a top quality internal format and allow you to edit and do production with almost no damage. You can then export as a new MP3 and the damage will only be that of your export. If you choose a crappy but tiny MP3 export, then you get a simple crappy MP3.

If you import a lesser quality MP3 (most internet music clips) Audacity will convert it along with its damage and allow you to perform production. It gets messy if you want to export a new MP3. If you choose a lesser quality MP3 for your new show, the two MP3 damages will add up. This is where you discover that you can't export your show without it sounding terrible.

If you instead choose a top quality MP3 export, the original MP3 damage will be preserved, no better or worse.. Nothing you do will make the show better than the worst MP3. If they're both bad, the damage adds.

Nobody ever posts top quality MP3 files, so people "borrowing" internet music for production always run into the dual compression damage problem. "I got my music from YouTube and now I can't make a small MP3 for my iPod. It sounds all bubbly and distorted."

Yes. It does. That's correct.

This, in a basket, is why doing production in MP3 is a terrible idea. Do everything in WAV or AIFF and produce the MP3 as a delivery step.

Koz