[clug] Audio file formats

[M at]

I use Sony minidisc as a complete and portable recording and editing
solution but this is not a Linux or open source solution.  If you want to
know more: http://walshm.site.net.au/matt/minidisc.htm.  Happy to answer any
questions.

Cheers,

M at .


On Tue, May 20, 2008 at 5:09 PM, Paul Wayper <paulway at mabula.net> wrote:

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> Kristy A. Bennett wrote:
> | Okay, CLUG-speak hasn't changed.  I understood about 56% of what you
> | were trying to convey as usual Paul!
> |
> | Paul Wayper wrote:
> |> So can you tell us what you're doing this for and what your end user
> |> will have
> |> to play the file back?  The more I understand what you're trying to do
> |> the
> |> better my advice will be :-)
> | I have had some requests from my business consultancy clients for some
> | materials that they can refer back to particularly on a range of topics
> | from IT issues, web security (or moreover web insecurity) through to
> | strategic HRM & marketing.  At the moment I provide hard copies of
> | information to them but there is an obvious demand out there for voice.
> | Many discussions have oriented around acquiring further information
> | through audio as it doesn't take as long to digest and can go into more
> | depth over the same time frame required to read a paper.  Add to that
> | the commute, morning walk or gym application and it's past the post.  At
> | this point I am looking for the best possible means to provide both,
> | what is in effect, a subscribed podcast with weekly releases as well as
> | CD's for them to throw in the car.
>
> OK, well this sounds like you need a reasonable quality podcasting setup.
>  If
> this is a commercial venture, you should be looking to buy some reasonable
> equipment for it.  I'd put together a list similar to:
>
> * One or two reasonable quality voice microphones with stands.  Shure,
> Alesis
> and Yamaha are good brands.
> * One four-track mixing board with at least two microphone inputs.  There
> are
> quite good small mixers made by Beringher under the Eurodesk brand.
> * One decent quality sound import/export box - preferably a USB or Firewire
> box that does at least 48KHz in 16bit stereo.  I like the look of the
> Edirol
> UA-1EX but haven't coughed up the money for one yet.
> * Cables to tie it all together.
> * More scratch hard disk space for all your audio.
>
> 1) Make sure your room is nice and quiet, and you (and your co-presenter or
> guest) have comfortable chairs close to microphones.
> 2) Make sure that the loudest sound the microphone is likely to hear is
> _just_
> below -3dB - just below the red line.
> 3) Record the sound in Audacity at the highest sampling rate and number of
> bits you can.
> 4) Save the audio as a rough cut now.
> 6) Process your sound to improve its quality.  At the very least you should
> normalise your sound.  You can also use the "Noise Removal..." effect in
> Audacity if you've got background noise - just select a section of audio
> where
> that background noise is the only sound and set that as the noise profile,
> then select the whole recording and run the noise removal on it.  You can
> also
> cut out those unnecessary 'um's and pauses if you're doing a question and
> answer session.  Trim the head and tail and put your intro and outro on.
> 7) Save that as a wave file in 44100Hz 16-bit stereo for the CD.
> 8) Use LAME to produce a high-quality and a small-size MP3 file of it for
> your
> website.  To get these I would recommend using:
>
> lame --abr 160 -q 1 -b 32 -B 320 -c $file.wav $file-high.mp3
> lame --abr 16 -a -q 2 -b 8 -B 160 --resample 11025 -c $file.wav
> $file-low.mp3
>
> On my test piece of music, we have:
> file.wav: 72MB
> file-high.mp3: 7.4MB = ~10x reduction.
> file-low.mp3: 798KB = ~100x reduction.
>
> The latter is still quite clear and would be perfectly listenable on an
> iPod.
> ~ I've had phone conversations that have sounded worse.
>
> If you want to go with 'standard' WAV files, then I would do the following:
>
> sndfile-resample -to 11025 -c 4 $file.wav /tmp/tempfile.wav
> sndfile-convert -ms-adpcm /tmp/tempfile.wav $file-low.wav
> rm /tmp/tempfile.wav
>
> (/tmp/tempfile.wav used due to the sndfile tools being unable to use stdin
> or
> stdout.  You can safely use linear interpolation (-c 4) here instead of the
> better quality -c 0 because we're just throwing out three out of four
> samples,
> and no actual re-engineering of the waveform need take place.)
>
> On the above file, this results in:
>
> file-low.wav: 4.6MB = ~20x reduction.
>
> This is, however, noticeably inferior in quality - the sound has less high
> notes and has a more noticeable crackle to it.  But, if people can't play
> MP3
> files or you're unwilling to write them, then this is your best bet.
>
> Of course, for OGG encoding for the same bitrates I would use:
>
> oggenc -b 160 $file.wav -o $file-high.ogg
> oggenc -b 16 --downmix --resample 11025 $file.wav -o $file-low.ogg
>
> These give:
>
> file-high.ogg: 6.9MB = ~10x reduction
> file-low.ogg: 966KB = ~80x reduction
>
> For a given bit rate, OGG is better in quality than MP3.
>
> What was I procrastinating about doing now?  Hope this helps, anyway :-)
>
> Have fun,
>
> Paul
>
> P.S. Don't forget to put in the artist, album, title etc tags in the MP3 or
> OGG files.
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