Package: abcde
Version: 2.3.99.6-1
Severity: wishlist
Says here:
% man abcde | grep -nA 5 LOWDISK | tail -n 6
456: LOWDISK
457- If set to y, conserves disk space by encoding tracks
immediately
458- after reading them. This is substantially slower than
normal
459- operation but requires several hundred MB less space to
complete
460- the encoding of an entire CD. Use only if your system is
low on
461- space and cannot encode as quickly as it can read.
Lines #460-461; it says "Use only if...". However, I've noticed there's
a second reason to use '-l'.
When a disk is badly scratched, ("abnormal operation"?), regular
'abcde' consistently tends to produce more read errors (e.g. 'V' in the
rip progress bar) than 'abcde -l' does. The '-l' makes the rip better
and often faster.
The cause is that 'cdparanoia' on a scratchy disk is quite timing
sensitive:
% zgrep -B 3 -A 15 shaking /usr/share/doc/cdparanoia/FAQ.txt.gz
delicate balance. In addition, a player is never distracted from what
it's doing... it has nothing else taking up its time. Now add a
non-realtime, (relatively) high-latency, multitasking kernel into the
mess; it's like picking up the player and constantly shaking it.
CDROM drives generally assume that any sort of DAE will be linear and
throw a readahead buffer at the task. However, the OS is reading the
data as broken up, separated read requests. The drive is doing
readahead buffering and attempting to store additional data as it
comes in off media while it waits for the OS to get around to reading
previous blocks. Seeing as how, at 36x, data is coming in at
6.2MB/second, and each read is only 13 sectors or ~30k (due to DMA
restrictions), one has to get off 208 read requests a second, minimum
without any interruption, to avoid skipping. A single swap to disc or
flush of filesystem cache by the OS will generally result in loss of
streaming, assuming the drive is working flawlessly. Oh, and virtually
no PC on earth has that kind of I/O throughput; a Sun Enterprise
server might, but a PC does not. Most don't come within a factor of
five, assuming perfect realtime behavior.
...so plain old 'abcde' which multitasks the encoding in the background
might consume every CPU clock. Thus 'cdparanoia' performance degrades,
it thrashes, and after several minutes gives up, and goes on to the
next equally troublesome sector. Whereas 'abcde -l'
lets 'cdparanoia' single task, (relative to encoding anyway), so
its performance becomes optimal.
Users: if you have a scratched disk that keeps getting 'V' errors,
try the '-l' switch, and the 'V's may be fewer or go away completely.
AND 'abcde -l' rips faster, because 'cdparanoia' doesn't get so badly
stuck on scratches.
The LOWDISK text in 'man abcde' should make a note of this. Apologies
to the maintainer for including no patch -- I couldn't think of a
succinct revision, (maybe later!), and this tip is so useful it
deserves to be public now.
-- System Information:
Debian Release: lenny/sid
APT prefers unstable
APT policy: (500, 'unstable')
Architecture: i386 (i686)
Kernel: Linux 2.6.18-4-686 (SMP w/1 CPU core)
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968) (ignored: LC_ALL set to C)
Shell: /bin/sh linked to /bin/dash
Versions of packages abcde depends on:
ii cd-discid 0.9-1 CDDB DiscID utility
ii cdda2wav 9:1.1.6-1 Dummy transition package for iceda
ii cdparanoia 3.10+debian~pre0-5 audio extraction tool for sampling
ii flac 1.1.2-6 Free Lossless Audio Codec - comman
ii speex 1.1.12-3 The Speex Speech Codec
ii vorbis-tools 1.1.1-11+b1 several Ogg Vorbis tools
ii wget 1.10.2-2 retrieves files from the web
abcde recommends no packages.
-- no debconf information
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