[GreenKeys] Saving RTTY art as audio

[David Ross]

greenkeyers -

Bob Camp wrote:
> 
> If I have a four hour tape and save it as binary it takes up about 80K 
> as straight file. If we zip the thing it will drop down to less than 30K 
> since the mapping is not very dense. A few thousand tapes will take up 
> 30 Megs on a web site. That's not to tough to find space for. Zip 
> compression is not lossy you loose nothing in the process.
> 
> If you do a normal audio CD then the same four hours will soak up 640 
> meg x 4 = 2.5 gigs. A reasonable compression probably drops that to 200 
> Megs. Since sound compression is lossy you don't want to crank it up to 
> far. MP3's are designed so the compression artifacts are not audible to 
> the human ear. The same may not be true of a TU ....
> 
> Run up as MP3's the thousand or so tapes would soak up 200 Gigs on the 
> web server. That's quite a bit more storage than the zip files.
> 
> It would be more practical to set up a java app that would take the 
> binary file and put out tones. That way you would have the best of both 
> worlds.
> 



I have been playing with exactly this -  converting ASCII text files to 
RTTY tones.  I run an ASCII text file through MMTTY to make Baudot audio 
tones, capture the audio tones to disk as a .WAV file, then convert the 
.WAV file to a .MP3 file using an .MP3 encoder.

   Running at 60WPM, 46,238 bytes of ASCII text converts into 8,140,640 
bytes of .MP3 audio, and that is done at 8Kbits/second -  every byte of 
ASCII text converts to 176 bytes of .MP3 audio.
   If the .WAV -> .MP3 conversion is done at 16Kbits/sec, then the file 
size is 16,280,719 bytes.
   All this for 2 hours and 15 minutes of 60WPM text -  not very 
efficient as far as disk space goes...

        46,238 bytes of .TXT files converts to
1,435,870,862 bytes of .WAV files (44.1 Ksample/sec, 16 bit stereo), or
     8,140,640 bytes of .MP3 files (at 8Kbits/second)

   The above conversions were made using 850 shift, but I would guess 
that 170 shift would give the same results.

   With my own conversions, I see no print errors at either 8Kbits/sec 
or 16Kbits/sec.
   Nor do I see any errors on George's Internet feed at 24Kbits/sec, 
either [Winamp -> MMTTY] or [Winamp -> Dovetron -> Model 28].  However, 
George's 24Kbps feed causes consistent underflows here, given a 26.4Kbit 
ISP connection.

   Using MMTTY to convert ASCII text to Baudot tones is the time 
bottleneck, being done in realtime as it is.
   The conversion from .WAV file to .MP3 file is quite fast -  I use the 
LAME 3.91 encoder -  free & reasonably fast, it runs in a DOS window.

   Is it really possible to do the text-to-tone conversion with a Java 
application?

Dave Ross    N7EPI