I recently bought a Rio 500 on eBay. While very happy with the device itself, I am convinced that, with some research (and your help), I can achieve the same or greater fidelity audio at smaller file sizes than I am currently have. For the purpose of this thread, my only concern is the best format/setting for "books on tape"/spoken word.

The device can read MP3, MPEG2.5, Audible AA (G.723), and ADPCM formats.

Right now, I covert a CD to mp3 format, using LAME alt-preset 80. This is considerably better sounding than any other LAME generated file (particularly the LAME ACM) [Thanks, Dibrom!]. And it generates files that are 114% the size of MP3pro 64Kb and 133% the size of AAC Psytel -Internet. While suprisingly competitive in file size, the quality of MP3pro and AAC is MUCH better sounding--particularly if the original audio had any hint of echo. In general, and particularly with echos, alt-preset 80 sounds significantly more "metallic", with overtones of a speech synthesizer. MP3pro and AAC, by contrast, are difficult to distinguish from the source material even on good quality speakers.

Quality-wise, I can withstand something as low as Audible 4 though I prefer better. In a perfect world, I would use AAC for high fidelity encodings (regular commute) or G.723 for extended duration encodings (long plane rides).

I know that knowledgable people on this board have said that LAME is intended for higher bit rate encodings and suggested MP3pro for these lower bit rate scenarios (given its smaller file size, I don't know why AAC wasn't suggested). However, until I figure out how to reprogram the Rio 500 codec or Sonic Blue releases firmware including either MP3pro or AAC (hah!), I don't have that option.

Therefore:
* I have spent a lot of time on this board but perhaps I missed a better LAME setting/MP3 encoder for spoken word?

* If not, can LAME be tweaked [hint, hint Dibrom]? I don't understand why LAME couldn't have a setting that beats any competitive MP3 encoder for spoken word.

* Alternatively, is there a means of encoding in MPEG 2.5 (which I believe will support lower bit rates) or G.723 that is as easy to do as MP3? I have found very little on the Internet regarding either of the latter formats, particularly with respect to generally available encoders as opposed to telecom implementations. I also searched specifically for an Audible format encoder, with no luck.

* Finally, if anyone knows of links to reprogramming the Rio 500 codec (which I understand to be a general purpose processor), I am interested, particularly with respect to AAC.

if you have to go with mp3 at low bitrates, try fhg instead of lame. at lower bitrates than 128, fhg performs better.

browse ff123's site, and i am sure you will be familiar with the different mp3 encoders and their pros/cons. http://www.ff123.net

here is a section from his site, at http://www.ff123.net/cbr128.html

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Fraunhofer MP3Enc31: This is the encoder which many people with good high frequency hearing would choose as the one to beat at CBR 128. Biggest shortcomings: 1) the default lowpass filter is set lower than other encoders (transition starts at about 14.5 kHz), such that people complain of a "muffled" sound. 2) There are occasional obvious dropouts/glitches in certain types of music (see my page "Dropouts in MP3/Alternate Codecs"). On the other hand, this codec does not "ring," meaning it does not produce artifacts caused by switching of high-frequency subbands (see my page, "What does ringing look like?"). And one can override the default lowpass filter. The switch settings I might try are:

-qual 9 -bw 16500

which will actually only extend the lowpass cutoff to about 16 kHz. Or, one can use the Alternate codec, which is a close relative of MP3Enc31, but which defaults to higher cutoff. Be sure not to use the bad version of the Alternate codec (see my page "Bug in older FhG Alternate Codec"). NOTE for NT (SP4 or later) or Win2K users: Using high values of -bw (greater than 16000) may cause a screeching high-pitched noise to be produced. It's a known bug in mp3enc31 when using those operating systems.

David Robinson has some information about what Fraunhofer themselves would recommend (see his post on r3mix's forum):

FhG suggest using FastEnc over MP3enc at bitrates up to 80kbps. I don't have a reference for this - I asked one of the FhG guys directly at the AES - they keep sending "reference" DOS mp3 encoders out to magazines, and I wondered which codecs they included - the answer FastEnc and mp3enc 3.1.1, the former up to 80kbps, the latter above it.

I believe mp3enc 3.1.1 to be what I term (actually what Cool Edit terms) "Alternate."



Fraunhofer FastEnc: In many cases, this encoder produces better (to my ears) sounding files at CBR 128 than MP3Enc31 and in some cases it beats Lame with - -nspsytune (in my opinion) On some songs with a lot of cymbals, lame has more of a tendency to flange than FastEnc. Be sure to use programs which don't use the bad version of this codec (see my page "Bug in Latest FhG FastEnc"). Some people with good hearing report hearing slight ringing, or a "steely" sound, as if the music had been placed in a metal room. This codec produces consistent quality, without the occasional obvious dropouts/glitches of MP3Enc31. Fraunhofer's VBR is based on FastEnc, and produces average bitrates near 128 kbit/s at the 50% quality level. See my page "MP3 codecs not recommended" for programs which properly implement Fraunhofer's VBR (there aren't many).

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talk with roberto about aac and portables. i am sure he knows more than anyone around here about that [except ivan of course...]


later
mike

Eheheh.

Well the most known portable that plays ISO AAC files is Philips Expanium. Others were reported to play it, but I never heard of tests. I'm aware of at least two people that played Psytel AAC in expanium, and worked well for them.

I don't know about links regarding Rio 500 programming. But if you ever find them, I suggest you contact Menno Bakker (www.audiocoding.com). He is already working on a fixed-point implementation of FAAD. He could help you program it.

Regards;

Roberto.

The Rio 500 does have a flash processor, but the Mp3 decoding part is handled by a fixed custom chip, so it cannot handle different formats.