problems converting MP3s to WAVs

[Net Llama!]

On 05/28/2005 05:52 AM, Klaus-Peter Schrage wrote:
> Net Llama! wrote:
>> On Fri, 27 May 2005, Klaus-Peter Schrage wrote:
>> 
>> 
>>>Net Llama! wrote:
>>>
>>>>On Fri, 27 May 2005, Klaus-Peter Schrage wrote:
>>>>
>>>>
>>>>>Sorry, Lonnni, there seems to be consistency in the way the line from
>>>>>mp3 to audio cd works:
>>>>>cdrecord needs an input which is 16 bit, stereo, 44100 Hz, uncompressed
>>>>>- usually a wav file. If it isn't, you have to make it like that. So, if
>>>>>your mp3 is already 44100 Hz, you're nearly done with a simple mpg321
>>>>>command. Otherwise, use a tool like sox or sndfile-resample (in the
>>>>>libsamplerate package) to fix the wav.
>>>>>Klaus
>>>>
>>>>
>>>>That seems to be my problem.  All of the MP3s are 32bit, instead of 16.  I
>>>>just scanned through the sox man page and didn't see anything obvious on
>>>>how to convert from 32 to 16 bits.  grrr.
>>>
>>>Can you put a sample mp3 somewhere so that I may have a look at it
>>>(can't promise anything, I'm not a sound expert)?
>>>Klaus
>> 
>> 
>> Sure, try this one:
>> http://netllama.linux-sxs.org/1.mp3
>> 
> 
> This sequence of commands turnes the initial file 1.mp3 (8.6 MB) into an 
> one track audio cd:
> 1) mpg321 -v -w 1_mo.wav 1.mp3
> 2) sox -V 1_mo.wav -r 44100 -c 2 1_fin.wav resample
> 3) cdrecord -v dev=/dev/hdc -pad 1_fin.wav
> 
> EXPLANATION short (a longer one might be worth a SxS ...)
> 
> 1) Using the -v option in mpg321 tells you what the initial file is all 
> about:
> 
> Freq: 22050
> mode: Single-Channel
> encoding: signed 16 bit
> Bitrate: 32 Kbits/s
> 
> What these figures mean:
> 
> - Frequency (aka: sample rate):
> Indicates how often a sample has been taken from the sound, it describes 
> the horizontal resolution.
> 
> - Mode:
> Of course, single-channel is otherwise called mono.
> 
> - Encoding:
> Describes the fineness of each of the samples, ie the vertical 
> resolution, in this case (signed) ranging from about -32000 to 32000.
> 
> - Bitrate:
> the overall data flow per second. Eg in CD audio, we have 16 bit, stereo 
> 44100 Hz, resulting in a bitrate of
> 44100 x 16 x 2 = 1411.2 Kbits/s.
> Common mp3 compression modes yield bitrates of 96, 128, 192 Kbits/s.
> 
> BTW: the filesize of the output wave file is 94.8 MB
> 
> 2) 1_mo.wav still is mono and has a horizontal resolution of 22050 Hz. 
> The sox command lifts this up to what cdrecord expects as input format:
> 44100 Hz, 16 bit, stereo.
> The 'resample' effect is not obligatory, but it is recommended to 
> enhance the rate conversion result.
> The output 1_fin.wav is, not unexpected, nearly exactly four times as 
> big as the input (1_mo.wav).
> 
> 3) The only remarkable option is -pad. It enlarges the input file to a 
> size which is a multiple of 2352, as data on an audio cd are stored in 
> chunks of 1/75 of a second:
> 44100/75 x 16 x 2 = 2352 Byte.

Thanks Klaus, that's exactly what I've been struggling with.

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
L. Friedman                       	       netllama at linux-sxs.org
LlamaLand		 		http://netllama.linux-sxs.org

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