Won't convert AA to MP3

[LtData]

Re: Won't convert AA to MP3

dMC r12 uses a different set of codecs. The DirectShow Decoder hasn't been ported to dMC r12 yet. All codecs that work with the beta are in the same thread where you downloaded dMC r12.

[Steve Cat]

Re: Won't convert AA to MP3

Well I'm not technical support and they seem to have quit monitoring this thread, but if it were me I'd just revert back to 11.5 unless there is some feature you love.

Anyway some thoughts:

Check your audible file for the text file for direct show that you made the .aa mod to. Once I did it on the wrong line and the //symbols prevent use.

I think Audible manager 5.0 leaves some files so after uninstalling it I moved my audio files so they wouldn't be deleted and completely deleted the Audible File folder and also completely unistalled DB Power amp and Direct Show and completely deleted the Illustrate folder. I ALSO UNISTALLED THE AUDIBLE WINDOWS MEDIA PLAYER 11 (Not the Media Player itself) DOWNLOAD MANAGER. The thingy that gives the little green box with the downward arrow in the system tray. Then I reinstalled Audible Manager 4.0
Power amp, and Direct Show and changed the extention to .aa in the notepad file. I DID NOT REINSTALL THE MEDIA PLAYER DOWNLOAD MANAGER.

I also deleted the the Audble files that were created in my documents user files as they are not deleted with the uninstall. BE CAREFUL NOT TO DELETE YOUR .aa files in the process.

Anyway, I think .aa support for DBPower amp is fragile at best, and things need to be perfect and Audbile is aware of it so they keep changing thier code to make it incom[patible. So my guess is that we'll have to constantly have to keep fooling with this. I really like my old Dell DJ mp3 player, but as soon as the San Disl e260 becomes compatible with .aa I might buy one. I saw one on sale at Walmart for $169, It has 4 megs. Good luck

[dhartson]

Re: Won't convert AA to MP3

OK, I got it working again. I uninstalled dMC r12 b4 and its codecs, and then installed dMC 11.5 again. Beforehand, in addition to the steps I had taken as of my last post, I downloaded from audible.com their "Audible Download Manager for Windows Media Player 11" from:

http://download.audible.com/AM50/AudibleDM_WMPSetup.exe

I am not sure that was necessary, but I mention it because it may (or may not) have been a factor in this working now with MediaPlayer11 (MP11); also, related to this, I "activated" MP11 to play Audible.com content by entering my Audible.com user ID and password.

Then (after re-installing dMC R11.5), I went back into dMC configuration and made sure that the DirectShow Codec showed up under the decoder tab with the .aa parameter. The *.aa files then showed up in the select files window properly, and conversion worked then without any more problems. (My only problem now is that the "pop up" tool tip isn't working anymore when viewing folders in Windows Explorer; I think I'll just view properties and not worry about it until after dMC R12 is released.)

Of interest on file size: I converted part 1 of an unabridged book with the following properties:
34.2 MB (format 3) 297:50 (m:sec), 15:1 compression ratio, 16000 frequency, 1 channel, 16 bits
dMC converted the file to mp3 (using Lame 3.96)
the resulting MP3 file:
107 MB, 267:55, 1200 frequency, 1 channel, 56Kbps bitrate

The conversion took 8 min., and the sound quality seemed comparable, but I don't know yet how much smaller we might make the MP3 files by lowering the specs on the conversion and keep a similar sound quality. I'd appreciate more feedback on this as more of us play with these settings.

Of course, a lot will depend upon what format of *.aa file you download from Audible since there is a huge difference between, say, format 1 (most highly compressed and lowest quality) and format 3. Their format 4 is supposed to compare favorably with an average MP3 file for music (like something encoded at 128 kbps, I think), but that is overkill on the spoken word and is double the size of format 3. On the other hand, those audio books with any kind of music used, like at the end of a chapter, are VERY annoying when using format 1, so I would recommend format 2 or 3 (and, of course, I use format 3). The point is, whichever of the audible formats is used will suggest how low the Lame encoder settings can be set before there is a further, significant loss in quality. The best quality would be obtained by downloading Audible's format 4, and then transcoding to whatever level of MP3 quality an individual finds acceptable. That is what I'd like more feedback on, since I ended up with a file 3x the size of the *.aa file in the format that best suits my preferences.

On players, my favorite was the old Rio 500, which did a great job of allowing a significant number of bookmarks, and had options to display the time remaining, would show the total time for the file, etc., and would "rewind" from part 2 of a book back into the end of part 1 of a book. Now, of course, it is obsolete . . .

Now, I'm off to experiment with Codec Central's "length splitter" utility to see how that might work to break down MP3 file sizes so that it is easier to navigate and "find my place" in a book. A very few CD players will start at the same spot that playback was last stopped, and I assume the same is true of some of the small MP3 players, but the one I use at present starts at the beginning of whatever file it was playing when playback is stopped, so a smaller file size is sort of critical (until I find a better player).

[dhartson]

Re: Won't convert AA to MP3

I think Audible manager 5.0 leaves some files so after uninstalling it I moved my audio files so they wouldn't be deleted and completely deleted the Audible File folder and also completely unistalled DB Power amp and Direct Show and completely deleted the Illustrate folder. I ALSO UNISTALLED THE AUDIBLE WINDOWS MEDIA PLAYER 11 (Not the Media Player itself) DOWNLOAD MANAGER. The thingy that gives the little green box with the downward arrow in the system tray. Then I reinstalled Audible Manager 4.0 Power amp, and Direct Show and changed the extention to .aa in the notepad file. I DID NOT REINSTALL THE MEDIA PLAYER DOWNLOAD MANAGER.

I also deleted the the Audble files that were created in my documents user files as they are not deleted with the uninstall. BE CAREFUL NOT TO DELETE YOUR .aa files in the process.

FIRST, I believe v5 is necessary (for me now, anyway) in order to download any more files from my "library" online at Audible.com after I upgraded to MediaPlayer11. This means having to uninstall v4 and install v5, and continue to switch back and forth between the versions in order to continue to purchase/download new content, and then convert to MP3. Consequently, I think it behooves us to keep close notes and determine the easiest and quickest way to reliably make the "switch". (Unless, of course, you want to go back to MP10.)

Comparing my experience to yours, it evidently is not necessary to completely delete the Audible folder when going back to AudibleManager v4 from v5. Nor did I completely delete the Illustrated folder. I didn't even delete the DirectShow codec since I learned (the hard way) that this codec is specific to dMC R11.5. Also, I did not delete any files in my documents user folder. Hopefully, and I will report back (it may be a while), a simple uninstall of AudibleManager version X and re-install of version Y (whichever direction, from v4 to v5, or the other way around), will be all that is necessary in the future to switch from downloading additional content (with v5), to transcoding to MP3 (with v4).

Evidently, based on your exerience, I may not have needed to install (or activate) Audible Download Manager for Windows Media Player 11, but I had read something in one of these threads that the system needs some kind of decoding codec from Audible that will allow the files to be played in MediaPlayer for any of this to work, and when I tried to play a *.aa file in MP11 I don't think it worked until after I installed the download manager specific to MP11. In any event, this won't affect switching back and forth between AudibleManager v4 and v5, so this will only document my experience for anyone else trying to get the transcoding to work in the first instance.

[Steve Cat]

Re: Won't convert AA to MP3

Well I'm sure your right I overdid the deleting thing. I was just going nuts trying to get it working and I was trying everything.

I am under the impression that THE thing I did to get it working was to uninstall the download manage. I too read that it needed to be installed, but when I unistalled it the .aa conversion worked. That's why I was so surprised. Are you saying that you had it installed and it ran?

FWIW Audible 4.0 works fine for downloading for me. I even use two separate login names and all files from both accounts show up under the 4.0 window.

As far a compression rates at the suggestion of FAzevedo I used 40 also with a quality 4 download and sound quality and file size were about the same. Getting larger files does not mean better quality than the original.

I really don't understand what you don't like about quality 4, are you saying that 2 or three are better sounding?

[dhartson]

Re: Won't convert AA to MP3

I have been working into the wee hours to the point that I am not entirely sure, but I am pretty sure that I downloaded and installed the Audible Download Manager for Windows Media Player 11, after which MP11 would play *.aa files.

I preferred AudibleManager v4 and only changed because I was no longer abler to download with v4; I preferred the way it allowed me to create a batch list of files to add to my MP3 player; with v5, it seems I have to add them one at a time. So, stick with v4 if it works for you!

As for the Audible file formats, format 4 is the best quality sound (described by Audible as "MP3 like"), and yes, in this case size does matter. Format 1 yields recognizable speech at about 2MB for 1 hr of content, and has basically been dropped for new content. Format 2 is of much better quality (described by Audible as being like AM radio) and is almost double in size (3.7MB for 1 hour of content). Format 3 is better still (described as FM quality), but how much better is open to personal interpretation; it is not quite double in size, with about 7.2MB for an hour of content. Format 4 is the best quality, but is again double in size, at 14.4MB for 1 hr. of content, and for plain speech it serves no purpose. On the other hand, if you have a fast connection, download and convert to MP3 and then delete the format 4 file, you will be starting with the best quality audio available and then can choose what quality (vs. file size) you want to end up with in your system or your player memory. There are some samples provided by Audible if you click the link at the top of your "library" listings; find the line:
"Learn more about devices & sound compression format."

I believe I will download in format 3 because I want to archive about 150 books and will encode in MP3 at a bit rate that is substantially lower than what format 3 is. As far as file size is concerned, as a general rule when going from a lossless file to a lossy compression scheme, the larger the file the less the compression and the less data that is tossed out, i.e., better quality. Now some codecs are better that others, so one may give you a better quality sound in a smaller file size than another. Also, what perhaps you were referring to about file size, is that once you have "tossed out" data in a lossy compression, there is no getting it back, so reencoding at a higher bit rate creates a larger file that is no better than what you started with -- it is just a waste of memory and time.

[Steve Cat]

Re: Won't convert AA to MP3

Darn, I had a long well reasoned reply to you post and somehow just deleted it, but the bottom line is that I'd sure like some audio expert or moderator to jump in here.

I was focusing on ultimate file size. The more I think about it the more I think your right. So the BAD NEWS is that any conversion of an .aa file to something other than wav or another lossless format, i.e., will result in worse quality, with the added problem of substantially larger files. I always thought audbile files were inherently bad, but the best I have listened to is quality 4 recompressed to a 190 bit rate. I really have never listened directly to an aa file other than through the speakers on my laptop. Before I complain further about audible quality I should listen to a conversion to wav on my mp3 player and .aa on my laptop with headphones.

[Steve Cat]

Re: Won't convert AA to MP3

No moderatator yet. I guess they don't like me since I asked for my money back, but I am still a registered customer......oh well.

Some conclusions listening through high quality enclosed ear headphones.

Obviously the best is the quality 4 .aa, however balance seems skewed to the right? Balance is ok during conversion and or compression even thou lame is set to stereo..........don.t know about conversion, it may be mono.

wav conversion, just not quite as crisp as .aa

190 bit rate lame, pretty darn close to wav........large file size

128 bit rate lame just a tad worse, but since I ha room on my mp3 player, I'd stick with 190 cause I'm fussy

48 bit rate, just to lazy at this point to take it further. Some noticeable distortion, probably not noticeable with ear buds or open ear headphones.
Tolerable is space is a problem, about the same file size 40 is probably the same file size as .aa

HOWEVER: Noticeable improvement, not up to 128 quality, but better if you convert to wav, then compress using razor lame or some such thing at 48 using the 3.97 codec! DBPoweramp uses an older lame codec, and may loose something in simultaneous conversion from .aa to mp3, so A little reatime eq of the wav file, say using something like transcribe or audacity makes it even better so if you want to do a little fooling around you can get file about the same size and acceptable quality.

conclusion: you're still better off using an aubible compatible player, but for the price you could buy 3-5 cd format audio books, or rent them, and convert them at 128-190 and you'd really have exeptional which may be the way I'm going to go , not sure at this point.

This product is certainly ok for free if you are willing to do the mp3 conversions yourself, or if you are lazy and want a simultaneos conversion, the $14 registration fee is fair, though I sure wish they'd work out whatever with lame

[Spoon]

Re: Won't convert AA to MP3

Make sure your frequencies are the same, or if different then enable the professional frequency conversion option.

[ChristinaS]

Re: Won't convert AA to MP3

You won't improve quality by increasing the bitrate.

So if the file that yu get after cinversion is considerably bigger than what yu started out with then you are using too high a bitrate. Filre sizes are quiet comparable given the same bitrate and channels no matetr what format you use - differnces are literally just a few bytes either way.

Granted yuo may not know the .aa bitrate as such - but you can calculate it easily. Use as a model 128kbps mp3 stereo = 1MB/minute of audio. Work it out in proportion.
What's the .aa file size / minute?

[Steve Cat]

Re: Won't convert AA to MP3

Make sure your frequencies are the same, or if different then enable the professional frequency conversion option.

Absolutely!

Note the .aa quality 4 files are generally 22050, not 44100.......conversion runs MUCH MUCH faster..............fwiw mono also

Thanks

[Steve Cat]

Re: Won't convert AA to MP3

You won't improve quality by increasing the bitrate.

So if the file that yu get after cinversion is considerably bigger than what yu started out with then you are using too high a bitrate. Filre sizes are quiet comparable given the same bitrate and channels no matetr what format you use - differnces are literally just a few bytes either way.

Granted yuo may not know the .aa bitrate as such - but you can calculate it easily. Use as a model 128kbps mp3 stereo = 1MB/minute of audio. Work it out in proportion.
What's the .aa file size / minute?

Well that's what I thought but then when he mentioned compressin g and already compressed file it got me messed up again, but what we are reallt doing is converting a compressed file so equivalent file sizes mean that no additional compression is taking place, at least in theory.

quality 4 .aa works out to 38.9 but at lame 40 encoding I hear a little what I would call phaser/flange distortion so I was using 56 but I'll try 48. Of course with normal earbuds on an mp3 player you probably wouldn't hear it. I was using my big can headphone off my laptop, now maybe the distortion is caused by the cheap integrated sound card, and I even hesitate to call it distortion since it isn't what I would call distortion like on a guitar, its a subtle wavering like a phase or flange pedal for guitar.

Learned alot.........thanks to all

[Steve Cat]

Re: Won't convert AA to MP3

One more thing, then I'll leave you alone. Moderators, don't you think you should note/respond to my experience with uninstalling the Media Player Download Manager as a solition to .aa conversion problems, two others have benefited from this trick.

[dhartson]

Re: Won't convert AA to MP3

I will make two lengthy, concurrent posts. The first will deal with some background information, my thoughts or speculation on Audible.com files, and my present transcoding recommendation.
The second will deal more strictly with the specifications of the files and the results of my efforts to strike a good balance on transcoding them to something that strikes a similar balance between audio quality and file size in order to archive the *.aa files to something that is more likely to be supported for a very long time.

This, then, is the first of the two concurrent posts.

By way of background -
Audible states of their file formats:
format 4 = 14.4 MB/hr (MP3-like)
format 3 = 7.2 MB/hr (FM radio)
format 2 = 3.8 MB/hr (AM radio)
format 1 = 2 MB/hr (fair)

It appears that Audible is dropping their support of format 1; it was their original format when the only player you could use was their proprietary player and most of us were downloading files over "dial up". As I recall, with the introduction of the Rio500 they began to sell the Rio and to offer the new formats (the Rio 500 played only formats 1 and 4). However, there were a few other players that were supported and so they provided the other, middle-range formats. As I have said before, I find that format 3 is a very acceptable compromise between quality of audio and file size for listening to what are predominately voice only files. Many books have no music, and the ones that do are usually only at a transition, as between chapters.

Since I have over 200 unabridged books at this point, I wanted to archive them in a format that is a little more reliable that relying on Audible.com to keep them available online in perpetuity, and since their proprietary file formats are a pain and, should Audible go by the board one day there would be no way to get around their DRM which requires a player, even the desktop player, to be "activated" online. Without them to "activate" the desktop player, like Windows MediaPlayer, a program like dMC is unable to access their content in order to transcode the file to another format.

My experience is that, when starting to transcode a *.aa file in dMC, Audible's little "Section Navigation" window appears.

This, by the way, brings up a completely different problem with transcoding their files. Audible places what amount to bookmarks in each of their proprietary file formats which they refer to as "sections"; I believe they are spaced about 45 minutes apart, often at the start of a chapter if a chapter break is somewhere near in time. A player that supports Audible.com files will allow a user to move forward or backwards through the file by chapter. When using Windows Media Player this navigation is done through Audible's little "Section Navigation" window.

*** N.B.:
(dMC may start transcoding a *.aa file in the middle!)

However, if you have used your desktop player to play the file you are going transcode, you will want to check on where the file will "open up" by double-clicking on it in Windows Explorer, or some other way, because the system will have kept track of what section you were in the last time you left off in listening to the file. When you start to transcode, dMC will only be able to transcode the file starting at that point where the Audible.com's "marker" is. So, when I first started to transcode the book that I have provided data on (in my second of these two concurrent posts), it started about 3 hours into the 10 hour book. I had to use the desktop player to get to the end of the file and play with the "Section Navigation" buttons until I closed the file and opened it again to find that the file began playing at the start. I then repeated the process one last time (clicking the "back" button in the "Section Navigation" window before closing the file again) to make sure that dMC would start at the beginning of the file. What was interesting is that I had downloaded the file in all four formats, and they ALL opened up well into the book. I don't recall if I made a "test listen" to them all, or if the system records the section and will open any of the formats to that point in the file. In any event, this is something to be aware of, particularly if you are going to batch convert any number of books!

*** (Recommendation)
The bottom line, I am satisfied with the results of transcoding *.aa files in a two-step process, starting with Audible's format 4 and transcoding to WAV files at 16 bit, 1 ch (mono), and a frequency of 22050 Hz. This goes quite fast; a 10 hour book in about 3 minutes (with dMC set to a priority of "Above Normal", which seems to be the default, and allows the use of the computer to do something light, like write an email or make a post.

The second step is to transcode the WAV file to a WMA file using the Windows Media Audio v9.1 codec from Codec Central (which appears to actually install v9.2, which I selected in the drop down window) with the following settings:
20kbps, 22kHz, mono CBR, 2 pass
This job took quite a bit longer, 19m:29s. However, the resulting file was more than adequate in audio quality, and the file size (90.7MB) was much smaller than Audible's format 4 file size (140MB), and was more comparable to the file size of Audible's format 3 file (70.5MB).

How much smaller the file might be made and retain an adequate sound quality is probably a matter that will vary greatly depending upon personal preferences, and a lot more experimentation. For the time being, I am satisfied with the settings I have recommended, but I would be very pleased to hear what the experience of others might be.

For the time being, all I need now is a portable player that will resume playing a WMA file at the point where it is stopped, instead of starting at the beginning of the file again. Any recommendations?

[dhartson]

Re: Won't convert AA to MP3

This is the second of two concurrent posts dealing with the specifications of Audible.com files (*.aa) and the data from trials of transcoding them to another, more easily supported file format. The goal is to find the ideal process and which encoder(s) and settings should be used.

I downloaded a book from Audible.com that was listed as 10 hrs long in each of the 4 available formats and used dMC to see what the specs were for each format. This is what I found:

format 1 = 34,008 bytes/min of audio (bpm)
10h:14m file = 19.9 MB or 20,881,523 bytes
File details per dMC:
Length (m:ss) 620:07
Size 20393KB
Uncompressed 581359KB
Comp. Ratio 28:1 (3%)
Frequency 8000
Channels 1
Bits 16
format 1 has _rev1_ in the file name

format 2 = 63,255 bpm
10h:20m file = 37.4 MB or 39,218,153 bytes
File details per dMC:
Length (m:ss) 620:06
Size 38299KB
Uncompressed 581343KB
Comp. Ratio 15:1 (6%)
Frequency 8000
Channels 1
Bits 16
format 2 has acelp85_ in the file name
Note well: acelp.net is a voice codec selection available under the WMA codec that installs from Codec Central, and the "8" comports with the 8000 Hz frequency reported by dMC; however, given the "5" in the "85" this would make a little more sense if the frequency was 8500 Hz, but the correlation is suggestive.

format 3 = 120,710 bpm
10h:13m file = 70.5 MB or 73,995,393 bytes
File details per dMC:
Length (m:ss) 613:54
Size 72262KB
Uncompressed 1151062KB
Comp. Ratio 15:1 (6%)
Frequency 16000
Channels 1
Bits 16
format 3 has acelp16_ in the file name
Note well: acelp.net is a voice codec selection available under the WMA codec that installs from Codec Central, and the "16" comports with the 16000 Hz frequency reported by dMC.

format 4 = 239,348 bpm
10h:13m = 140 MB or 146,959,870 bytes
File details per dMC:
Length (m:ss) 613:49
Size 143516KB
Uncompressed 1586092KB
Comp. Ratio 11:1 (9%)
Frequency 22050
Channels 1
Bits 16
format 4 has mp332_ in the file name
Note well: the mp3 reference suggests that Audible used a MP3 codec to transcode their original sound track; however, the "32" suggests that they used a frequency of 32000 Hz, but dMC reports that the file was created at 22050 Hz.

===============================================

I provided the bytes/min in response to the inquiry of a moderator, Christina, who has offered some advice to assist in this quest.

I had previously searched all the posts in the forum for recommendations on the ideal settings for transcoding Audible.com files and this is what I found:

Re: Converting Audible to mp3

http://forum.dbpoweramp.com/showthread.php?t=11045&highlight=audible

Posted query:
I was able to convert a couple of files but one thing I noticed was that the Audible files are incredibly compressed compared to the mp3.
The audible files come in mono, 22050 mhz frequency and 32 kbps (according to iTunes info) but they still sound pretty good. I tried converting them to mp3 several times over, but unless I was doing at least 80kbps (usually 96) on the lame encoder the result was noticably lower quality. The 32kbps lame setting was almost unlistenable.
The converted output, as a result, ends up being about 3x the size. Does audible have a kick-ass compression algorithm, is something lost in the conversion, or is the lame encoder not doing as well as it might?
Just curious.
Thanks
_Mark
Inaudible

Moderator's Response:
09-03-2006, 06:22 PM
ChristinaS
dBpowerAMP Moderator
The mp3 format isn't as good at lower bitrates as would be the wma format.
I dont' know how that stacks up against audible though.

I know wma at 32kbps, unless you need hi-fi, is quite decent, and comparable to mp3 at 64kbps.

I suspect though you need to manage the frequency as well.

At low bitrate a lower frquency is better. If you converted to mp3 at 44.1KHz and low bitrate that would sound worse than if you kept the frequency at 22Khz for instance.

------------------------

http://forum.dbpoweramp.com/showthread.php?t=10316&highlight=audible

04-18-2006, 02:42 PM
Try converting to wave, keep the frequency the same during any conversion.
Spoon

-------------------------

http://forum.dbpoweramp.com/showthread.php?t=9146&highlight=audible

10-18-2005, 12:49 PM
Re: Converted large MP3 loses minutes

I think you should do the conversion in several steps.
First convert to mono, keep bitrate and frequency as asource.
Then convert this resulting file to a different bitrate, and keep channels and frequency as souce.
Finally convert this latest resulting file to a different frequency, keep the channels and bitrate as source.
__________________
Christina

-------------------------

http://forum.dbpoweramp.com/showthread.php?t=7506&page=3&pp=15&highlight=audible

04-16-2005, 01:55 PM
Posted query:
I've always wondered. audio cassette is like 22khz right?
Which sounds better 22khz at 128kbps or 44khz at 64kbps?
Regards.

Moderator's comment:
I was just experimenting with some combinations and I found that at very low bitrates a lower frequency sounds better, at least for wma formats.
So 20-32 kbps CBR sounds better, brighter, at 22KHz than at 44Khz. Above 32kbps 44Khz is better.
(Don't forget in wma, those low bitrates result in about twice as good an audio file than mp3 at the same bitrates. So 32kbps wma is about as good as mp3 at 64kbps - buit only half the file size).
__________________
Christina

===============================================

So, that is all the information available to me through the forum and the data provided by dMC. I started to experiment with transcoding and kept the following log:

format 3 encoded to WAV at default settings
Above Normal priority - 14m:09s
30x Real-time Encoding
Problem: the file started encoding about 3 hrs into the file due to

Audible's "placemark" (see comments in the first of these two posts)
after much "fiddling"-

trying again, 16 bit, 44100Hz (CD), 1 ch (mono)
20m:18s - success! but a VERY large file:
3.02GB (3,248,079,704) 3,171,953KB

now, trying at 16000Hz
sending to "Converted Music" folder to avoid overwriting

(since they will have the same file name)
3m:46s (161x Real-time Encoding)
1.09GB (1,178,441,644 bytes); 1,150,822KB
quite quick work, and the resulting file is of good quality

finally, using the format 4 file, & 22050 Hz
fast! 2m:55s & 210x Real-time encoding!
1.51GB (1,624,066,604) 1586003KB
given that the sound quality is superior, and the file size is not that much larger (about 50% larger), I will use format 4 for my project of converting my library to a more easily used format for archival purposes. Thus -

=====================================

Conclusion:

I settled on starting with format 4 and converting to
WAV at 22050Hz (16 bits, 1 channel/mono)

next, experimenting with encoding to WMA or MP3 (Lame):

- based on Christina's comments, and the available options for mono transcoding,
I will start with WMA, 20kbps, 22kHz, mono CBR, 2 pass
results:
19m:29s job time
90.7 MB file
- quality is just fine for listening to a voice
- this is NOT a music file, but any sections with some transitional music will not offend by any means
- how much smaller we might take it remains to be seen

I find this to be quite satisfactory.

What I'd like to know from the more experienced members of this community is their insight based on my speculations on Audible's different file formats, particularly format 4, and whether a different frequency should be used when converting to WAV format. Is the data from dMC (frequency of 22050 Hz) reliable, or might they have used 32000 Hz as suggested by their file name?

I would also like to know what settings other members of these forums may prefer so that I might try them before starting the archival of my files, a very time consumming project!