SqueezeCenter and upsampling

In order to upsample 16/44.1 stream to, for example, 24/96 and play it on the Transporter you need:

• Download, compile and install SoX (Sound eXchange)
• Tweak convert.conf in the slimserver root directory. It can contain the following:
flc flc * *
[sox]  -v0.995 –buffer 32768  -t flac -r44100 -2 -c2 $FILE$ -t flac -C0 -3 -c2 -r96000 – polyphase -cutoff 1.0

ape flc * *
[MAC] $FILE$ – -d | /usr/local/bin/sox  -v0.995 –buffer 32768  -t wav -r44100 -2 -c2 – -t flac -C0 -3 -c2 -r96000 – polyphase -cutoff 1.0

mp3 flc * *
[lame] –mp3input –decode –silent $FILE$ – | [sox] -v0.995 –buffer 32768 -t wav -r$RATE$ -2 -c2 – -t flac -C0 -3 -c2 -r96000 – polyphase -cutoff 1.0

wvp flc * *
[wvunpack] $FILE$ -wq –skip=$START$ –until=$END$ -o – | [sox] -v0.995 –buffer 32768 -t wav -r44100 -2 -c2 – -t flac -C0 -3 -c2 -r96000 – polyphase -cutoff 1.0

• Restart SqueezeCenter
• Click on Settings (SqueezeCenter GUIU)
• Go to Advanced-> File Types
• Disable what you don’t need

Comments:

Input file parameters
Output file parameters
-v – volume adjustment
-t – file format
-r44100 – sample rate
-c2 – two channels
-2 – 16bit
-3 – 24bit
-C0 – no compression
polyphase – upsampling algorithm

Please note:

• you have to convert 24/96 stream to FLAC, because SlimDevices Transporter has two issues with WAV format:
  • plays 96kHz stream too slow
  • does not recognize 24 bit stream

  (see here)

• Polyphase algorithm  is VERY CPU intensive. Don’t be surprised if your CPU is under 100% load.
# top
. . .
PID USERNAME LWP PRI NICE SIZE RES STATE TIME CPU COMMAND
19683 root 1 0 4 8052K 4356K run 0:03 77.23% sox
. . .

# prtdiag
. . .
Version Location Tag
——————————– ————————–
Intel(R) Xeon(R) CPU X5355 @ 2.66GHz CPU1
. . .

Now how it all sounds. The difference is subtle (again, in my system!) but can be described as rough (16/44.1) vs. treated with sandpaper (upsampled to 24/96) surface. More liquid, “rounded up”, with more air between the images with no “splinters” No, not “night and day” but easier to listen. Like a good power cable but for free 😉

More on upsampling:

• An analysis of sample rate conversion in Sox
• Performance of audio resampling software