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John J. Stimson-III
2005-02-16, 17:00
I guess I am chiming in a bit late to this discussion, but I was
fiddling with my oscilloscope and the Squeezebox all yesterday.

It all started when I did some level-matched listening tests between
the Squeezebox analog outputs and my California Audio Labs CL-2500
CD/DVD player (which is one kick-ass CD player). I was doing so
mainly to decide whether I needed to buy an external DAC for the
Squeezebox, since it will replace the CL-2500 as my primary music
source.

In non-ideal test conditions (I have a mild cold, and I had to turn
the source switch myself), they seemed pretty similar. Score one for
the "all properly engineered digital sources sound alike"
crowd...until: on one track (Karan Casey, "The World Turned
Upside-Down (the Diggers' Song)") I noticed that with the Squeezebox
selected I could hear very loud and clear some cymbals in the left
channel. With the CL-2500, the cymbals were more muted and towards
center. I also tried a CAL DX-1 (their basic model CD player, using a
Panasonic single-chip controller/DAC), which sounded more like the
Squeezebox. Interesting -- the two "low-end" players bring out those
cymbals more. I was worried that the CL-2500 might be broken somehow,
since it didn't match the other two.


Time to break out the oscilloscope. My worries about the expensive
DVD player being broken were laid to rest, because sine wave test
tracks displayed in X-Y mode produced near-perfect straight sharp
lines (actually a slight loop at higher frequencies indicating a small
delay between channels), and the length was identical at all
frequencies. In V vs time mode, the CL-2500 produced nice smooth sine
waves, with a slight envelope modulation at the very highest
frequencies (near 21kHz). In contrast, the Squeezebox showed a
fuzzier line (noise? harmonic distortion?) which increased in length
between 17kHz and 21kHz. The modulation envelope was quite severe at
frequencies near 21kHz. And the waveforms were piecewise-continuous,
with J-shaped decay curves between samples which looked like little
bites had been taken out of the wave. Apparently there's not much or
any analog filtering on the DAC output in the Squeezebox.

When I measured the DX-1, it had continuous looking sine waves and the
modulation at high frequencies was somewhere in between the CL-2500
and the Squeezebox.

I really can't draw any conclusions linking these objective
observations to the qualitative sound, since the DX-1 sounded more
like the Squeezebox but measured more like the CL-2500. I also
measured the speaker outputs, and the little jaggies in the
Squeezebox's output are nicely rounded off by the time the signal
makes its way through my crossover and power amp.

Having gone through all that, I can think of worse insults for a piece
of hardware than "It sounds like a CAL DX-1."

I am, however, going to use an outboard DAC. I've read very good
things about the MSB Link series, the Bel Canto DAC-1 and DAC-2, and
the Musical Fidelity A324. In terms of older gear, the 24/96 versions
of the CAL Sigma and Alpha DACs should be pretty good, comparable to
my CL-2500, and Meridian has a good reputation for their CD players.

I just found a screaming deal on an MSB "Nelson" Link III at
Sound4Sure in Aptos, California. Check their "refurbished" section,
the stuff is all half price, which puts the base model Link III at
$250!

Enough for now...

--

john (AT) idsfa (DOT) net John Stimson
http://www.idsfa.net/~john/ HMC Physics '94