View Full Version : Audio Books or Voice Tracks

09-22-2004, 08:01 AM
I am interested in being able to listen to a CD which contains many books, presentations, et cetera read by various people, which are available on the Internet.

Since the demands of voice are low compared to music, the Bit Rate can be much lower than 32 Kbps, for example, the files I am most interested in listening to are 16 Kbps.

The difficulties that I run into are 2:

-The 16 Kbps files are encoded as MP3 (MPEG2 Layer3 half rate mode).

For the 16 Kbps file encoded as MP3 (MPEG2 Layer3 half rate mode) to play in my MP3 player, I need to convert the file to MP3 (MPEG1 Layer3) or MP3 (LAME).

-When using dBpower AMP Music Converter, the only option available for the conversion target file is 32 Kbps.

This raises the voice file size from 4676 KB to a converted voice file size of 17,689 KB increasing the size of the file by almost 4 times.

This greatly reduces the number of files that can be put on to one disk and multiplies the number of disks that would have to used to hold the files.

Is it possible to convert a 16 Kbps MP3 (MPEG2 Layer3 half rate mode) to a 16 Kbps MP3 (MPEG1 Layer3) that would be about the same file size?

09-22-2004, 03:47 PM
have you tried the "speex" codec? see on this page and download/install http://www.dbpoweramp.com/codec-central-speex.htm

09-22-2004, 04:10 PM
I think he has a CD player that can play mp3 tracks. If you select mono you can get lower bitrates.

09-25-2004, 01:29 AM
Thank you for your replies.

I do have an MP3 player and have finally figured out what the problem was.

I will detail it here just in case it might help anyone else out.

For an MP3 to be considered to be an MP3 (MPEG1 Layer3), it must be encoded at 44100 Hz or 44.1 kHz.

Otherwise the MP3 will be considered to be an MP3 (MPEG2 Layer3), an MP3 (MPEG2 Layer3 half rate mode), et cetera.

This means that when an MP3 is encoded at:

8000 Hz or 8 kHz = MP3 (MPEG2 Layer3)
11025 Hz or 11.025 kHz = MP3 (MPEG2 Layer3)
12000 Hz or 12 kHz = MP3 (MPEG2 Layer3)
16000 Hz or 16 kHz = MP3 (MPEG2 Layer3)
22050 Hz or 22.050 kHz = MP3 (MPEG2 Layer3)
24000 Hz or 24 kHz = MP3 (MPEG2 Layer3)
32000 Hz or 32 kHz = MP3 (MPEG2 Layer3)

My MP3 player will not play MP3 (MPEG2 Layer3) it will only play = MP3 (MPEG1 Layer3).

I had thought that the file being classified as an MP3 (MPEG2 Layer3) was based on the Kbps.

It seems that this is not correct.

In dBpower AMP Music Converter, starting at 24000 Hz or 24 kHz and lower, the lower Kbps rates of 25 Kbps, 16 Kbps and 8 Kbps are offered.

However, due to the fact that the encoding will be at 24000 Hz or 24 kHz, the file will then result in and be classified as an MP3 (MPEG2 Layer3) no matter what the Kbps rate is.

dBpower AMP Music Converter does offer encoding at 32000 Hz or 32 kHz, but the Kbps rate of 32 Kbps will be the lowest Kbps rate allowed.

However, The resulting file will still be an MP3 (MPEG2 Layer3) because the encoding is taking place at 32000 Hz or 32 kHz and the Kbps rate has no effect on whether the file is classified as an MP3 (MPEG2 Layer3) or an MP3 (MPEG1 Layer3).

As I wrote earlier, the encoding must take place at 44100 Hz or 44.1 kHz for the MP3 file to be classified as an MP3 (MPEG1 Layer3).

In dBpower AMP Music Converter, based on 44100 Hz or 44.1 kHz, the lowest Kbps rate allowed is 32 Kbps.

Success occurs at this point and the MP3 file is now classified as an MP3 (MPEG1 Layer3),

As long as the MP3 is encoded at 44100 Hz or 44.1 kHz and 32 Kbps or a higher Kbps rate, then the result is an MP3 (MPEG1 Layer3).

The only 2 questions left are the following:

-Is it possible to encode an MP3 at 44100 Hz or 44.1 kHz and 16 Kbps or a lower Kbps rate?

-Is it possible to convert MP3s to the above?

09-25-2004, 06:26 AM
Is it possible to encode an MP3 at 44100 Hz or 44.1 kHz and 16 Kbps or a lower Kbps rate?

-Is it possible to convert MP3s to the above?

I believe the short answer is "no" to both, if by the term "mp3" we mean files created within MPEG1 Layer 3 standards. These standards are, to the best of my knowledge):

All Layers may use 32, 44.1 or 48 kHz sampling frequency.

All Layers are allowed to work with similar bitrates:
Layer-1: from 32 kbps to 448 kbps
Layer-2: from 32 kbps to 384 kbps
Layer-3: from 32 kbps to 320 kbps
(where the layers are MPEG1, Layer 1; MPEG1, Layer2 and MPEG1, Layer3
Source: http://www.faqs.org/faqs/compression-faq/part2/section-2.html

The bigger question, however, is your mp3 player. What can it play, what can it not play? If it can handle a backwards compatible MPEG2 file encoded as an mp3 file, you should be ok. But it might not be able to play an mpeg1, layer 3 encoded at 44.1 khz and 32 kbs (or, even more likely, at 32khz and 32 kbs).
I would think your best bet might be either check the documentation for your player or to use some trial and error to see what your mp3 player can handle and what it cannot.
Best wishes,
Bill Mikkelsen

09-26-2004, 12:50 AM
The best solution would be to buy another MP3 portable... ;) If it really only supports 44.1 kHz as a valid sample rate for MPEG-1 Layer III, it's simply broken, because the allowed sample rates for that format are 32, 44.1 and 48 kHz.

Another good source of information are the FAQs from the MPEG Audio Subgroup at the University of Hannover:


Yet another one might be the Wiki of Audiocoding.com:


angus aberdeen
01-16-2006, 07:24 PM
I have had the similar problem with audio files being MPEG-2 Audio Layer 3 and not the desired MPEG-1 Audio Layer 3 format. Similar to the previous post, it is because the sample rate was at 16000Hz and not the 44100Hz. The Sony mp3 player i just recently bought (all of them in fact) will only play MPEG-1 Layer 3 44100Hz mp3 files.

Has anyone found a good converter that will take mp3 16000Hz files and convert them to mp3 MPEG-1 44100Hz files? I have about 300+ hour long files to process.

Thanks ahead of time.

01-16-2006, 10:22 PM
Has anyone found a good converter that will take mp3 16000Hz files and convert them to mp3 MPEG-1 44100Hz files?
Your implication is that dBpowerAMP Music COnverter cannot handle this conversion.

To do this, you will want to enable Professinal Frequency Conversion (which is set in dMC Configuration as an Option; go Start>All Programs>dBpowerAMP Music Converter>Configuration>dBpowerAMP Music Converter Configuration). Please be sure that you do not enable the option to delete source files after conversion.

If you did this, what were your results?
If they were unsatisfactory, what bitrate, bit and channel settings did you use for your converted mp3 files?

If the conversion attempt failed, see if you can do a test conversion of your 16 kHz mp3. This is the same as a regular conversion except that where you select your output format you select "Test Conversion (No Write)". This will not create an output file but it will either very rapidly tell you it did test convert successfully (meaning it can read the file, an necessary step to the conversion process) or it will tell you that the conversion failed (meaning the program cannot read the file and thus is highly unlikely to be able to convert the file).

Best wishes,