I've seen some concerns expressed over the processing power of the SBT, so I thought I'd do a little experiment.

First, my setup is Netgear ReadyNAS Duo with LMS -> SBT (with all Soundcheck mods applied except -k, buffersize 4000us) -> Chord QBD76 (with full (4 sec) buffering, although this doesn't seem to work on hi-res). 100Mbps wired Ethernet.

I tried a variety of music (all classical) of differing bit rates as you'll see below.

I used 'top' to measure CPU activity. Its fairly lightweight, taking only about 2% max CPU. I used 2 sample rates: 20 secs to get a rough average and 2 secs to try to observe peaks.

Please note that these are all observed so please don't take them as definitive. They are the best I could do quickly (I did take a number of samples of each though).

So the results:

  • Beethoven Piano Concerto 5 'Emperor' - 1. Allegro - Emil Gilels, Philharmonia Orchestra, EMI Classics

16bit/44.1kHz
FLAC file downloaded to SBT as FLAC - 678kbps VBR

  • 20 sec sample - approx 75-80% idle, 5-10% sirq
  • 2 sec sample - min idle 71%, max sirq 12%
FLAC file converted to PCM on NAS and then downloaded to SBT as PCM - 678kbps VBR (converted to 1411kbps PCM)

  • 20 sec sample - approx 75-80% idle, 10-15% sirq
  • 2 sec sample - min idle 67%, max sirq 22%
  • Beethoven Piano Concerto 5 'Emperor' - 1. Allegro - Artur Pizaro, Scottish Chamber Orchestra, Linn

24bit/96kHz

FLAC file downloaded to SBT as FLAC - 2467kbps VBR

  • 20 sec sample - approx 25-40% idle, 30-50% sirq
  • 2 sec sample - min idle 38%, max sirq 60%

PCM file downloaded to SBT as PCM - 4608kbps CBR

  • 20 sec sample - approx 10-15% idle, 55-75% sirq
  • 2 sec sample - min idle 0%, max sirq 80%
  • Pergolesi Concerto Grosso no 12 'La follia' per archi e cembalo, I Musici, Fone Records

24bit/96kHz
FLAC file downloaded to SBT as FLAC - 3024kbps VBR

  • 20 sec sample - approx 20-45% idle, 30-50% sirq
  • 2 sec sample - min idle 0%, max sirq 95%
PCM file downloaded to SBT as PCM - 4608kbps CBR

  • 20 sec sample - approx 5-20% idle, 55-75% sirq
  • 2 sec sample - min idle 0%, max sirq 93%
  • Mozart Symphony No. 38 in D major (‘Prague’), K.504 - I Adagio - Allegro - Scottish Chamber Orchestra, Linn

24bit/88.1kHz

FLAC file downloaded to SBT as FLAC - 2477kbps VBR

  • 20 sec sample - approx 35-45% idle, 30-40% sirq
  • 2 sec sample - min idle 21%, max sirq 50%
PCM file downloaded to SBT as PCM - 4233kbps CBR

  • 20 sec sample - approx 10-20% idle, 60-70% sirq
  • 2 sec sample - min idle 1%, max sirq 76%
One observation. The sirq-net-rx/0 process made up most of the sirq figure.

I don't feel qualified to comment precisely on the above. Broadly, however, the SBT CPU appears to struggle with hi-res PCM, but maybe its still OK. Is SqueezOs real-time embedded Linux and if so, is it designed to cope? Does its own buffering eliminate these problems?

I normally run my setup with FLAC->PCM conversion taking place on the NAS for 16/44.1 files and, through experience, use hi-res PCM files because the NAS struggles with the conversion. It generally sounds pretty good to me, although I haven't compared FLAC vs PCM on the SBT. One small issue is that I get a very small amount of 'crackling' on the Pergolesi track (above), but not on any other hi-res albums that I've noticed.

Chris