Mp3 saves at an EXTREMELY large file size

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Mp3 saves at an EXTREMELY large file size

Permanent link to this post Posted by surfingaliens » Thu Mar 15, 2012 3:01 am

I am recording a podcast and when I export it to mp3 it saves at a very large file size (an hour long recording saved at 64 kbps is 25MB) IS there anything I can do to reduce it. I have searched and found no problem like this one. I have also tried to uninstall and reinstall audio and to no avail.
I have several recorded pieces that do the same thing. I have even tried reducing to mono. No Luck!

Any Help would be appreciated
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Re: Mp3 saves at an EXTREMELY large file size

Permanent link to this post Posted by steve » Thu Mar 15, 2012 12:37 pm

If you're exporting at 64kbps CBR (constant bit rate) then there will be 64kb of data for every second of audio.
64 kb = 8 kB
1 hour = 3600 seconds
1 hour at 64 kbps = 3600 x 8 = 28800 kB = (about) 28 MB

A 64 kbps stereo track will share the bits between the left and right channels so there will be 32 kbps for the left channel and 32 kbps for the right channel.
A 64 kbps joint stereo track will use some bits to represent the data that is common to both channels, and some of the bits to represent the difference between the two channels.
If much of the audio is the same in left and right channels then "joint stereo" will produce better sound quality than "stereo" because most of the bits are available for the audio that is common to both channels.
A 64 kbps mono track will use all 64 kb of data for that one audio channel.
32 kbps mono will use 32 kb of data per second for one channel - roughly the same per channel as 64 kbps stereo.

Try converting the track to mono in Audacity, then export as 32 kbps (it does not matter if "stereo" or "joint stereo" are selected when you export a mono track).
This should produce a file that is roughly half the size that you are getting now.
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Re: Mp3 saves at an EXTREMELY large file size

Permanent link to this post Posted by surfingaliens » Thu Mar 15, 2012 12:57 pm

Thank You, that explains alot. The problem I am having is still the audio is too large. I have used Audacity in the past and recorded tracks just as long or longer and when I export them to mp3, the size isn't even 1MB.
I can't figure out what the difference is. Does it occur when I'm recording? If so what settings should I be using?

Thanks in advance
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Re: Mp3 saves at an EXTREMELY large file size

Permanent link to this post Posted by steve » Thu Mar 15, 2012 1:44 pm

surfingaliens wrote:when I export them to mp3, the size isn't even 1MB.

Perhaps you were looking at the size of the Audacity .AUP file. The .AUP file is the "Audacity Project File" and it does not contain any audio data - it is just a text (XML) file that tells Audacity how to arrange the audio data in the Project.

Perhaps you were looking at much shorter recordings?

The arithmetic speaks for itself.
"64 kbps" is "64 kb (kilobit) per second" which is "8 kB (kilobyte) per second" so that's around 28 MB per hour.
1 MB for an hour of audio would be 1024/60 kB per minute = 1024/3600 kB per second = 0.2844 kB per second = (less than) 3 bits per second which is not enough to produce any audio. A "bit" is a "binary digit" - a "1" or a "0".
It is not possible to define one second of audio with only three "bits".
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Re: Mp3 saves at an EXTREMELY large file size

Permanent link to this post Posted by skyy38 » Thu Mar 15, 2012 11:21 pm

surfingaliens wrote:I am recording a podcast and when I export it to mp3 it saves at a very large file size (an hour long recording saved at 64 kbps is 25MB) IS there anything I can do to reduce it. I have searched and found no problem like this one. I have also tried to uninstall and reinstall audio and to no avail.
I have several recorded pieces that do the same thing. I have even tried reducing to mono. No Luck!

Any Help would be appreciated


Sometimes, a direct, outside solution can help:

http://media.io/

Give this a shot with one of yhour podcasts and see how it works out.
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Re: Mp3 saves at an EXTREMELY large file size

Permanent link to this post Posted by steve » Sat Mar 17, 2012 6:27 pm

skyy38 wrote:Sometimes, a direct, outside solution can help:

Not in this case.
You can't cheat the math.
Even at the highest MP3 compression (very low quality) an hour of audio requires about 3.4 MB.
8kbps = 1kB per second
1 hour = 3600 seconds
I hour at 8kbps = 3600000 bytes = (about) 3.4 MB
9/10 questions are answered in the FREQUENTLY ASKED QUESTIONS (FAQ)
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