Hi,
there is an interesting case when the FLAC encoder (using 1.2.0) is
given simple waves. Simple waves means: I have a list of {frequency,
duration, pause} tuples that define the monophonic tune. In other
words, exactly one frequency is played at a time.
This is the original dataset from 1989 (driving a PC speaker back
then):
$ ls -l ihold.sd
-rw-r--r-- 1 jengelh users 20616 Aug 14 00:57 ihold.sd
Since driving the PC speaker is mostly a privileged operation these
days, one would just convert it to PCM and use soundcard output. The
program "sd" I have written does just that. The two numerical
parameters a and b denote the square and sine rate.
# 0:1 rate <=> 0% square, 100% sine generation
$ ./sd ihold.sd 0 1 | sox -r48000 -s -w -t raw - ihold-sine.wav
# 1:2 rate <=> 33% square, 66% sine generation
$ ./sd ihold.sd 1 2 | sox -r48000 -s -w -t raw - ihold-square1-sine2.wav
# 1:0 rate <=> 100% square, 0% sine generation
$ ./sd ihold.sd 1 0 | sox -r48000 -s -w -t raw - ihold-square.wav
Now this is what happens when encoding to FLAC:
$ flac -8 ihold-sine.wav
ihold-sine.wav: wrote 2422225 bytes, ratio=0.353
$ flac -8 ihold-sine2-square1.wav
ihold-sine2-square1.wav: wrote 5474921 bytes, ratio=0.798
$ flac -8 ihold-square.wav
ihold-square.wav: wrote 5573016 bytes, ratio=0.813
As soon as square waves are mixed in, the FLAC compression ratio
drops rapidly up to the point where it equals the ratio of typical
day-to-day music.
While I do not request FLAC to compress the wave back to its original
20KB, I think it could improve on the sine and square compression.
Are there any plans to address this?
If you would like to have the data files and/or transformation
program for testing, let me know and I'll upload :)
thanks,
Jan
--
--- Jan Engelhardt <jengelh@computergmbh.de> wrote:> Hi, > > > there is an interesting case when the FLAC encoder (using 1.2.0) is > given simple waves. Simple waves means: I have a list of {frequency, > duration, pause} tuples that define the monophonic tune. In other > words, exactly one frequency is played at a time. > > This is the original dataset from 1989 (driving a PC speaker back > then): > > $ ls -l ihold.sd > -rw-r--r-- 1 jengelh users 20616 Aug 14 00:57 ihold.sd > > Since driving the PC speaker is mostly a privileged operation these > days, one would just convert it to PCM and use soundcard output. The > program "sd" I have written does just that. The two numerical > parameters a and b denote the square and sine rate. > > # 0:1 rate <=> 0% square, 100% sine generation > $ ./sd ihold.sd 0 1 | sox -r48000 -s -w -t raw - ihold-sine.wav > > # 1:2 rate <=> 33% square, 66% sine generation > $ ./sd ihold.sd 1 2 | sox -r48000 -s -w -t raw - > ihold-square1-sine2.wav > > # 1:0 rate <=> 100% square, 0% sine generation > $ ./sd ihold.sd 1 0 | sox -r48000 -s -w -t raw - ihold-square.wav > > Now this is what happens when encoding to FLAC: > > $ flac -8 ihold-sine.wav > ihold-sine.wav: wrote 2422225 bytes, ratio=0.353 > > $ flac -8 ihold-sine2-square1.wav > ihold-sine2-square1.wav: wrote 5474921 bytes, ratio=0.798 > > $ flac -8 ihold-square.wav > ihold-square.wav: wrote 5573016 bytes, ratio=0.813 > > As soon as square waves are mixed in, the FLAC compression ratio > drops rapidly up to the point where it equals the ratio of typical > day-to-day music. > > While I do not request FLAC to compress the wave back to its original > 20KB, I think it could improve on the sine and square compression. > Are there any plans to address this?hard to say what is happening without seeing the files. FLAC does have a run-length encoding mode so with pure square waves it is possible to get very high compression with a custom encoder. Josh ____________________________________________________________________________________ Got a little couch potato? Check out fun summer activities for kids. http://search.yahoo.com/search?fr=oni_on_mail&p=summer+activities+for+kids&cs=bz
On Aug 15 2007 15:21, Josh Coalson wrote:>> >> there is an interesting case when the FLAC encoder (using 1.2.0) is >> given simple waves. Simple waves means: I have a list of {frequency, >> duration, pause} tuples that define the monophonic tune. In other >> words, exactly one frequency is played at a time. >> >> Now this is what happens when encoding to FLAC: >> >> $ flac -8 ihold-sine.wav >> ihold-sine.wav: wrote 2422225 bytes, ratio=0.353 >> >> $ flac -8 ihold-square.wav >> ihold-square.wav: wrote 5573016 bytes, ratio=0.813 >> >> As soon as square waves are mixed in, the FLAC compression ratio >> drops rapidly up to the point where it equals the ratio of typical >> day-to-day music. >> >> While I do not request FLAC to compress the wave back to its original >> 20KB, I think it could improve on the sine and square compression. >> Are there any plans to address this? > >hard to say what is happening without seeing the files. FLAC does >have a run-length encoding mode so with pure square waves it is >possible to get very high compression with a custom encoder.http://jengelh.hopto.org/ihold-sine.wav http://jengelh.hopto.org/ihold-square.wav have fun, Jan --