Bugzilla – Bug 2586
Background noise streaming AAC from Linux-based Slimserver
Last modified: 2008-09-15 14:38:10 UTC
Overview Description: When I listen to quiet music at reasonable amplification either through my Squeezebox 2 or SoftSqueeze, I hear background digital noise. This can only be descirbed as a wind or sea like sound. The music still plays, but quiet pieces sound distorted, whereas louder parts sound acceptable. In short, I guess I could say that I seem to have a reduced signal to noise ratio. In comparison, if I listen to the same AAC file through iTunes, or decode the file manually to WAV using faad (faad -o outfile.wav infile.m4a) and play that, then the quality is perfect. I get the same problem if I set the player settings with or without rate limiting (i.e. transcoding via lame, or sending the signal raw). All my AAC files are ripped from CDs using iTunes with standard settings. Steps to Reproduce: Install a PC with Fedora Core 4 using the standard Server installation but with the following package groups also installed: Development tools; Legacy Software Development. Disable firewall and selinux. I have an ext3 partition on the server which holds all my music and is mounted at /usr/local/music. This is shared using Samba so that I can access this from my Windows XP PC to add / remove music on the server. Once Fedora Core is installed and fully patched, I install Slimserver as follows: # rpm -i slimserver-*.noarch.rpm # cd /usr/local/slimserver/Bin/ # ./build-perl-modules.pl Just hit return for default values while the additional modules compile... I then install faad2 and lame using the following process: # cd /etc # rm -f yum.conf # wget http://www.fedorafaq.org/samples/yum.conf # rpm -Uvh http://www.fedorafaq.org/yum # yum install faad2 lame Now I edit convert.conf: # vi /usr/local/slimserver/convert.conf Comment out lines: #mov aif * * # [mov123] $FILE$ Add the following lines to the end of the file: # Transcoding for AAC files. mov mp3 * * [faad] -w -f 2 $FILE$ | [lame] --resample 44100 --silent -q $QUALITY$ -b $BITRATE$ -r - - mov aif * * [faad] -w -f 2 $FILE$ I now start slimserver with: # service slimserver start Then I point the server at /usr/local/music and ask it to scan the folder for music. This takes 30 minutes or so (I have 6000+ songs). Actual Results: Play any song using either softsqueeze or slimbox 2 (although quiet music shows the problem most obviously) and turn your amplifier up to a reasonable level. You should hear a hissing / digital noise in the background. Expected Results: No hissing noise. This is possible if I manually decode an AAC file using the faad linux command into a wav, and then play this through slimserver. The effect is demonstrated in these two files: http://myweb.tiscali.co.uk/textengine/slim/track1.wma http://myweb.tiscali.co.uk/textengine/slim/track2.wma I have recorded these by linking the analogue output of my PC to the line in; playing the tracks using softqueeze; and recording using the Microsoft plus analogue recorder. Track 1 is the wav file I converted using faad from the original AAC. Track 2 is the original AAC. Unfortunately I could only record the right channel due to a lack of cables, but you can certainly hear the problem clearly in track 2. Build Date & Platform: I have tested this using a clean Fedora Core 4 linux installation and Slimservers 6.1.1 and 6.2.1. Additional Builds and Platforms: I can also reproduce this on a SUSE 10.0 linux desktop running the Pearl source as the server. Additional information: See discussion forum thread http://forums.slimdevices.com/showthread.php?t=18219 for original discussion.
This sounds like earlier complaints involving interference via wireless. Some SB2 units early in the build cycle were improved with an additional cap. Have you contacted support@slimdevices.com?
Subject: Re: Background noise streaming AAC from Linux-based Slimserver Hi Thanks for the quick feedback. I can, however, confirm that my problem is not related to EMI interference of any kind. I can hear the noise if I stream - over wired Ethernet - from my Linux slimserver to my Windows XP PC running softsqueeze. Additionally, I hear the noise when I stream an AAC in this way, but I do not hear the noise if I stream a WAV in the same way. My opinion is that the noise is being introduced digitally somwhere between faad decoding the AAC, and my squeezebox or softsqueeze playing it. The question is, of course, where? Regards Nick. Slim Devices Bugzilla wrote: >https://bugs-archive.lyrion.org/show_bug.cgi?id=2586 > > > > > >------- Comment #1 from slim-mail@deane-freeman.com 2005-11-17 09:10 ------- >This sounds like earlier complaints involving interference via wireless. Some >SB2 units early in the build cycle were improved with an additional cap. Have >you contacted support@slimdevices.com? > > > > >------- You are receiving this mail because: ------- >You reported the bug, or are watching the reporter. > > > >
This problem has been reproduced in a second set-up as described in the discussion forum here: http://forums.slimdevices.com/showthread.php?t=18219&page=4 The set-up used is as follows: Ubuntu/SB2/6.2 Branch 5187/faad Thanks Nick.
I have also reproduced this using Fedora Core 4 Linux with faad2-2.0-0.lvn.5.3 and slimserver 6.2.1 - 5119 - Linux - EN - utf8. I hand-converted the test.m4a file to test.wav using faad on the same system where slimserver is running and loaded both files on the slimserver. I then compared the two files in SoftSqueeze: 1) test.m4a 2) test.wav #1 exhibits the problem (like "whooshing" or as someone said, "waves crashing") #2 sounds good #2 should have passed through the same conversions as #1. The only difference I can see is that #1 is transcoded by slimserver using faad via convert.conf, whereas #2 was hand-converted. Mysterious.
I need to upgrade the severity of this bug to 'critical' since it significantly affects audio quality. It would be good to get some confirmation soon if this is indeed a software issue, or if alternative solutions are available. Thanks.
https://bugs-archive.lyrion.org/page.cgi?id=fields.html#bug_severity Critical crashes, loss of data, severe memory leak Major major loss of function
Is this an x86-64 server? Can you run with --d_source to make sure that faad is being called correctly? Are these Apple Lossless, or lossy AAC?
Questions: Is this an x86-64 server? Can you run with --d_source to make sure that faad is being called correctly? Are these Apple Lossless, or lossy AAC? ------------------------ Answers: The hardware I am running on is a Dell Latitude CPx H500GT laptop (Pentium III 500 Mhz; 256 Mb RAM), and I have also reproduced this on my Dell Dimension 3000 desktop (Celeron D 2.8 GHz; 1 Gb RAM). The AACs I am playing are all lossy, ripped at 128kbps using iTunes on Windows XP. The output from SlimServer using the --d_source option is as follows: ----------------------------------------------------> [root@slimlinux slimserver]# ./slimserver.pl --d_source 2005-11-23 07:04:53.7286 loading conversion config files... 2005-11-23 07:04:53.7308 input: 'mov' output: 'mp3' clienttype: '*': clientid: '*': '[mov123] $FILE$ | [lame] --resample 44100 --silent -q $QUALITY$ -b $BITRATE$ -r - -' 2005-11-23 07:04:53.7319 input: 'ogg' output: 'mp3' clienttype: '*': clientid: '*': '[sox] -t ogg $FILE$ -t raw -r 44100 -c 2 -w -s $-x$ - | [lame] --resample 44100 --silent -q $QUALITY$ --abr $BITRATE$ -r - -' 2005-11-23 07:04:53.7327 input: 'wav' output: 'mp3' clienttype: '*': clientid: '*': '[lame] --resample 44100 --silent -q $QUALITY$ --abr $BITRATE$ $FILE$ -' 2005-11-23 07:04:53.7336 input: 'aif' output: 'mp3' clienttype: '*': clientid: '*': '[lame] --resample 44100 --silent -q $QUALITY$ --abr $BITRATE$ $FILE$ -' 2005-11-23 07:04:53.7344 input: 'shn' output: 'mp3' clienttype: '*': clientid: '*': '[shorten] -x $FILE$ - | [lame] --resample 44100 --silent -q $QUALITY$ --abr $BITRATE$ - -' 2005-11-23 07:04:53.7353 input: 'flc' output: 'mp3' clienttype: '*': clientid: '*': '[flac] -dcs --skip=$START$ --until=$END$ -- $FILE$ | [lame] --resample 44100 --silent -q $QUALITY$ --abr $BITRATE$ - -' 2005-11-23 07:04:53.7361 input: 'wma' output: 'mp3' clienttype: '*': clientid: '*': '[wmadec] -r 44100 -b 16 -n 2 $FILE$ | [lame] -x --resample 44100 --silent -q $QUALITY$ --abr $BITRATE$ - -' 2005-11-23 07:04:53.7370 input: 'mpc' output: 'mp3' clienttype: '*': clientid: '*': '[mppdec] --raw-le --silent --prev --gain 3 $FILE$ - | [lame] -x --resample 44100 --silent -q $QUALITY$ --abr $BITRATE$ - -' 2005-11-23 07:04:53.7379 input: 'ape' output: 'mp3' clienttype: '*': clientid: '*': '[mac] $FILE$ - -d | [lame] --resample 44100 -x --silent -q 9 --abr $BITRATE$ - -' 2005-11-23 07:04:53.7387 input: 'mp3' output: 'mp3' clienttype: '*': clientid: '*': '-' 2005-11-23 07:04:53.7394 input: 'aif' output: 'aif' clienttype: '*': clientid: '*': '-' 2005-11-23 07:04:53.7402 input: 'wav' output: 'wav' clienttype: '*': clientid: '*': '-' 2005-11-23 07:04:53.7409 input: 'shn' output: 'wav' clienttype: '*': clientid: '*': '[shorten] -x $FILE$ -' 2005-11-23 07:04:53.7417 input: 'flc' output: 'wav' clienttype: '*': clientid: '*': '[flac] -dcs --force-raw-format --endian=little --sign=signed --skip=$START$ --until=$END$ -- $FILE$' 2005-11-23 07:04:53.7425 input: 'ogg' output: 'aif' clienttype: '*': clientid: '*': '[sox] -t ogg $FILE$ -t raw -r 44100 -c 2 -w -s $-x$ -' 2005-11-23 07:04:53.7433 input: 'wma' output: 'wav' clienttype: '*': clientid: '*': '[wmadec] -r 44100 -b 16 -n 2 $FILE$' 2005-11-23 07:04:53.7441 input: 'mpc' output: 'wav' clienttype: '*': clientid: '*': '[mppdec] --raw-le --silent --prev --gain 2 $FILE$ -' 2005-11-23 07:04:53.7449 input: 'ape' output: 'wav' clienttype: '*': clientid: '*': '[mac] $FILE$ - -d' 2005-11-23 07:04:53.7456 input: 'mpc' output: 'aif' clienttype: '*': clientid: '*': '[mppdec] --raw-be --silent --prev --gain 2 $FILE$ -' 2005-11-23 07:04:53.7465 input: 'wma' output: 'wma' clienttype: 'squeezebox2': clientid: '*': '-' 2005-11-23 07:04:53.7473 input: 'flc' output: 'flc' clienttype: '*': clientid: '*': '-' 2005-11-23 07:04:53.7481 input: 'aif' output: 'flc' clienttype: '*': clientid: '*': '[flac] -cs --totally-silent --compression-level-0 --skip=$START$ --until=$END$ -- $FILE$' 2005-11-23 07:04:53.7489 input: 'wav' output: 'flc' clienttype: '*': clientid: '*': '[flac] -cs --totally-silent --compression-level-0 --skip=$START$ --until=$END$ -- $FILE$' 2005-11-23 07:04:53.7500 input: 'shn' output: 'flc' clienttype: '*': clientid: '*': '[shorten] -x $FILE$ - | [flac] -cs --totally-silent --compression-level-0 --endian little --sign signed --channels 2 --bps 16 --sample-rate 44100 -' 2005-11-23 07:04:53.7510 input: 'ogg' output: 'flc' clienttype: '*': clientid: '*': '[sox] -t ogg $FILE$ -t raw -r 44100 -c 2 -w -s $-x$ - | [flac] -cs --compression-level-0 --totally-silent --endian big --channel 2 --bps 16 --sample-rate 44100 --sign signed -' 2005-11-23 07:04:53.7520 input: 'wma' output: 'flc' clienttype: '*': clientid: '*': '[wmadec] -r 44100 -b 16 -n 2 $FILE$ | [flac] -cs --totally-silent --compression-level-0 --endian little --sign signed --channels 2 --bps 16 --sample-rate 44100 -' 2005-11-23 07:04:53.7529 input: 'mpc' output: 'flc' clienttype: '*': clientid: '*': '[mppdec] --silent --prev --gain 2 $FILE$ - | [flac] -cs --totally-silent --compression-level-0 -' 2005-11-23 07:04:53.7538 input: 'ape' output: 'flc' clienttype: '*': clientid: '*': '[mac] $FILE$ - -d | [flac] -cs --totally-silent --compression-level-0 -' 2005-11-23 07:04:53.7548 input: 'mov' output: 'flc' clienttype: '*': clientid: '*': '[mov123] $FILE$ | [flac] -cs --totally-silent --compression-level-0 --endian big --sign signed --channels 2 --bps 16 --sample-rate 44100 -' 2005-11-23 07:04:53.7557 input: 'mp3' output: 'mp3' clienttype: 'transcode': clientid: '*': '[lame] --resample 44100 --silent -q $QUALITY$ --abr $BITRATE$ $FILE$ -' 2005-11-23 07:04:53.7566 input: 'flc' output: 'flc' clienttype: 'transcode': clientid: '*': '[flac] -dcs --skip=$START$ --until=$END$ -- $FILE$ | [flac] -cs --totally-silent --compression-level-0 -' 2005-11-23 07:04:53.7576 input: 'mov' output: 'mp3' clienttype: '*': clientid: '*': '[faad] -w -f 2 $FILE$ | [lame] --resample 44100 --silent -q $QUALITY$ -b $BITRATE$ -r - -' 2005-11-23 07:04:53.7584 input: 'mov' output: 'aif' clienttype: '*': clientid: '*': '[faad] -w -f 2 $FILE$' 2005-11-23 07:05:27.9667 Adding song index 0 to song queue 2005-11-23 07:05:27.9671 Clearing out song queue first 2005-11-23 07:05:27.9674 Song queue is now 0 2005-11-23 07:05:27.9685 c6:dc:9b:f1:0b:62: Switching to mode stop from stop 2005-11-23 07:05:27.9688 Already in playmode stop : ignoring mode change 2005-11-23 07:05:28.1889 c6:dc:9b:f1:0b:62: Switching to mode stop from stop 2005-11-23 07:05:28.1897 Already in playmode stop : ignoring mode change 2005-11-23 07:05:28.1903 jumping to 4 2005-11-23 07:05:28.1909 Adding song index 4 to song queue 2005-11-23 07:05:28.1914 Clearing out song queue first 2005-11-23 07:05:28.1920 Song queue is now 4 2005-11-23 07:05:28.1932 c6:dc:9b:f1:0b:62: Switching to mode play from stop 2005-11-23 07:05:28.1956 openSong on: file:///usr/local/music/Kate%20Bush/Aerial_%20A%20Sky%20of%20Honey/2-05%20Sunset.m4a 2005-11-23 07:05:28.2078 openSong: getting duration 359, size 5743183, endian and offset 0 for file:///usr/local/music/Kate%20Bush/Aerial_%20A%20Sky%20of%20Honey/2-05%20Sunset.m4a 2005-11-23 07:05:28.2097 Setting maxBitRate for softsqueeze01 to: 0 2005-11-23 07:05:28.2108 Setting maxBitRate for softsqueeze01 to: 0 2005-11-23 07:05:28.2169 Setting maxBitRate for softsqueeze01 to: 0 2005-11-23 07:05:28.2179 Setting maxBitRate for softsqueeze01 to: 0 2005-11-23 07:05:28.2186 undermax = 1, type = mov, softsqueeze = c6:dc:9b:f1:0b:62, lame = /usr/bin/lame 2005-11-23 07:05:28.2195 checking formats for: mov-flc-softsqueeze-c6:dc:9b:f1:0b:62 2005-11-23 07:05:28.2200 checking formats for: mov-flc-*-c6:dc:9b:f1:0b:62 2005-11-23 07:05:28.2205 checking formats for: mov-flc-softsqueeze-* 2005-11-23 07:05:28.2210 checking formats for: mov-flc-*-* 2005-11-23 07:05:28.2216 Checking to see if mov-flc-*-* is enabled 2005-11-23 07:05:28.2221 enabled 2005-11-23 07:05:28.2226 Found command: [mov123] $FILE$ | [flac] -cs --totally-silent --compression-level-0 --endian big --sign signed --channels 2 --bps 16 --sample-rate 44100 - 2005-11-23 07:05:28.2253 drat, missing binary mov123 2005-11-23 07:05:28.2261 checking formats for: mov-aif-softsqueeze-c6:dc:9b:f1:0b:62 2005-11-23 07:05:28.2267 checking formats for: mov-aif-*-c6:dc:9b:f1:0b:62 2005-11-23 07:05:28.2272 checking formats for: mov-aif-softsqueeze-* 2005-11-23 07:05:28.2277 checking formats for: mov-aif-*-* 2005-11-23 07:05:28.2282 Checking to see if mov-aif-*-* is enabled 2005-11-23 07:05:28.2287 enabled 2005-11-23 07:05:28.2292 Found command: [faad] -w -f 2 $FILE$ 2005-11-23 07:05:28.2319 Setting maxBitRate for softsqueeze01 to: 0 2005-11-23 07:05:28.2329 Setting maxBitRate for softsqueeze01 to: 0 2005-11-23 07:05:28.2336 Matched Format: aif Type: mov Command: [faad] -w -f 2 $FILE$ 2005-11-23 07:05:28.2342 openSong: this is an mov file: file:///usr/local/music/Kate%20Bush/Aerial_%20A%20Sky%20of%20Honey/2-05%20Sunset.m4a 2005-11-23 07:05:28.2348 file type: mov format: aif inrate: 125 maxRate: 0 2005-11-23 07:05:28.2353 command: [faad] -w -f 2 $FILE$ 2005-11-23 07:05:28.2377 Using command for conversion: "/usr/bin/faad" -w -f 2 "/usr/local/music/Kate Bush/Aerial_ A Sky of Honey/2-05 Sunset.m4a" & | *********** Ahead Software MPEG-4 AAC Decoder V2.0 ****************** Build: Jun 16 2005 Copyright 2002-2004: Ahead Software AG http://www.audiocoding.com Floating point version This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. ************************************************************************** /usr/local/music/Kate Bush/Aerial_ A Sky of Honey/2-05 Sunset.m4a file info: LC AAC 358.282 secs, 2 ch, 44100 Hz title: Sunset artist: Kate Bush writer: Kate Bush album: Aerial: A Sky of Honey genre: Rock track: 5 totaltracks: 9 date: 2005 compilation: tempo: 00000 BPM tool: iTunes v6.0.1.3, QuickTime 7.0.3 iTunNORM: 0000013B 00000155 0000123D 000014CC 00053251 00048011 00007FFF 00007FFF 00051FB8 00049FF6 iTunes_CDDB_IDs: 9+128B0234BBF0070821FE6A269DC28C7F+6409380 --------------------- | Config: 2 Ch | --------------------- | Ch | Position | --------------------- | 00 | Left front | | 01 | Right front | --------------------- 2005-11-23 07:05:28.2836 Streaming with format: aify of Honey/2-05 Sunset.m4a. 2005-11-23 07:05:28.3437 c6:dc:9b:f1:0b:62 New play mode: play 2005-11-23 07:05:28.3568 c6:dc:9b:f1:0b:62: Current playmode: play 2005-11-23 07:05:28.6318 Got a track starting event 2005-11-23 07:05:28.6326 Song 4 has now started playing 2005-11-23 07:05:28.6338 Song queue is now 4 2005-11-23 07:05:42.8644 c6:dc:9b:f1:0b:62: Switching to mode stop from play4a. 2005-11-23 07:05:42.8649 c6:dc:9b:f1:0b:62 New play mode: stop 2005-11-23 07:05:42.8654 Stopping and clearing out old chunks for client c6:dc:9b:f1:0b:62 2005-11-23 07:05:42.8681 Resetting song queue 2005-11-23 07:05:42.8686 Song queue is now 4 2005-11-23 07:05:42.8692 c6:dc:9b:f1:0b:62: Current playmode: stop Decoding /usr/local/music/Kate Bush/Aerial_ A Sky of Honey/2-05 Sunset.m4a took: 15.14 sec. 23.66x real-time. [root@slimlinux slimserver]# <---------------------------------------------------- It looks like faad is being called correctly, but I'm no expert! Let me know if you need anything else.
Actually, I have repeated this test to verify one other thing. Currently, I am using the following entry in convert.conf to play the AAC files: mov aif * * [faad] -w -f 2 $FILE$ And if I change this to the following (which is the recommended setting in the Slimserver wiki) all I hear is loud digital white noise: mov wav * * [faad] -w -f 2 $FILE$ I have just dumped the debug output from Slimserver when using "mov wav * *" and it appears the same faad command is being used as with "mov aif * *": <SNIP> 2005-11-23 08:07:57.6216 Checking to see if mov-wav-*-* is enabled 2005-11-23 08:07:57.6223 enabled 2005-11-23 08:07:57.6228 Found command: [faad] -w -f 2 $FILE$ 2005-11-23 08:07:57.6255 Setting maxBitRate for softsqueeze01 to: 0 2005-11-23 08:07:57.6265 Setting maxBitRate for softsqueeze01 to: 0 2005-11-23 08:07:57.6272 Matched Format: wav Type: mov Command: [faad] -w -f 2 $FILE$ 2005-11-23 08:07:57.6278 openSong: this is an mov file: file:///usr/local/music/Kate%20Bush/Aerial_%20A%20Sky%20of%20Honey/2-05%20Sunset.m4a 2005-11-23 08:07:57.6284 file type: mov format: wav inrate: 125 maxRate: 0 2005-11-23 08:07:57.6289 command: [faad] -w -f 2 $FILE$ 2005-11-23 08:07:57.6313 Using command for conversion: "/usr/bin/faad" -w -f 2 "/usr/local/music/Kate Bush/Aerial_ A Sky of Honey/2-05 Sunset.m4a" & | 2005-11-23 08:07:57.6510 Streaming with format: wav I don't have a full understanding of how convert.conf works, but it is intersting that "mov wav" and "mov aif" appear to call faad in identical ways, yet the audio output is very different. I assume then that the output from faad must pipe back into Slimserver to then be sent across the network to Squeezebox or Softsqueeze. This being the case, then perhaps it is at this stage that the background noise is being introduced when "mov aif" is used. Just my thoughts. Nick.
mov aif and mov wav are the same command, but different 'endian' (detected by server for wav vs aif) The noise you hear is the result of incorrect endian. mov wav should probably be -f 1
Subject: Re: Background noise streaming AAC from Linux-based Slimserver Thanks. I actually tried mov wav with -f 1 and it made no difference to the noise. Still, I guess this is irrelevant to the problem in hand. Nick. >------- Comment #10 from slim-mail@deane-freeman.com 2005-11-23 09:12 ------- >mov aif and mov wav are the same command, but different 'endian' (detected by >server for wav vs aif) The noise you hear is the result of incorrect endian. >mov wav should probably be -f 1 > >
In a spare moment I have just installed and tested SlimServer 6.2.1 on Windows XP. I can confirm that this platform does not suffer from the noise I have heard when using SlimServer on Linux. As such this problem appears to be a Linux-specific issue. Nick.
Hi Would it be possible to get a brief status update on this bug? It would at least be good to know if you guys at Slimdevices have managed to reproduce these symptoms. If there is any additional information you need from me then please feel free to ask. Thanks Nick.
I've been messing around again this afternoon and have got a little closer to figuring out the root cause of this problem. It appears not to be the Slimserver per se, but appears instead to be the act of transcoding from AAC to another format via the stdio. I have performed a number of tests, with the following results: 1. Decode an AAC file to a WAV. COMMAND USED: faad infile.m4a outfile.wav RESULT: When I play the .wav using windows media player, there is no noise. 2. Encode the .wav from test 1 into an MP3 manually. COMMAND USED: lame infile.wav outfile.mp3 RESULT: When I play the .mp3 using windows media player, there is no noise. 3. Transcode an AAC to MP3 via stdio COMMAND USED: faad -w infile.m4a | lame - outfile.mp3 RESULT: When I play the .mp3 using windows media player, the music plays but with the same background noise as seen when listening via my Squeezebox and Softsqueeze. CONCLUSION: From the tests above, there seems to be a limitation when transcoding from AAC to another format via stdio. As a result, using this method of transcoding with Slimserver will introduce an unacceptable level of background noise. As this is the transcoding method Slimdevices recommend when running Slimserver on a Linux server, I believe this is not an acceptable solution. What can be done to work-around this problem? Thanks Nick.
This issue has been fixed by manually patching and re-compiling faad2 to fix a bug in that programme's code. As such this Slimserver bug should now be closed. I would, however, advise that the documentation on setting-up a linux SlimServer to play AAC files is reviewed and updated. My experience has shown that there are a number of problems which must be overcome that are not mentioned on the SlimDevices web site. All information is available on my forum post.
Thanks! Feel free to update the wiki with the information you feel is necessary to get other users going again: http://wiki.slimdevices.com/index.cgi?AAC