In theory, then, supplying an equivalent TTL signal to the CD player’s DAC circuitry, direct from the Sonos and Squeezebox wireless music players, would allow me to compare the CD and wireless players' performance back to back.

So I did exactly that, bought a coaxial to TTL digital signal converter (coaxial has lower voltage than TTL) and plumbed each of the wireless systems directly into the DAC half of the CD player.Next I encoded around fifteen CDs into the open source lossless FLAC compression format and settled down to a good long listening test.

First up was a back-to-back comparison of the Sonos and Slim Devices systems using their coaxial S/PDIF outputs. Neither the choral strains of Mozart’s Requiem, the intense bass punch and electronic sounds of The Prodigy’s Girls nor Diana Krall’s soft jazz standards revealed any kind of disparity between the two. I couldn’t hear any difference.


Here you can see the digital input from the wireless device, converted from coaxial to TTL, connected directly to the DAC circuitry on the Unico CD.


Next, I used my £250 Denon DVD-2910 and the Squeezebox, again output via coaxial digital output, to compare CD with FLAC over wireless. And this time there was a small difference. Instruments seemed to stand out a little more with the CD, boosting the sound staging with the breathy vocals of Diana Krall standing out in particular, but importantly, I was hard pushed to say whether this was as a result of a slightly higher output from the DVD player, or whether the sound was a quantifiable improvement. Fiddling with the volume levels between players seemed to iron the differences out.

Finally, came the big test – comparing back to back with the CD player in its original state, and here the difference was more noticeable. Both with the Sonos ZP80 and Squeezebox as source components, the sound wasn’t quite as dynamic as it was with the CD player. The piano of Ben Folds cut the air with the high end player in a way that the same sound from the FLAC file over wireless just didn’t. Andreas Scholl’s piercing vocals filled the room better and sounded richer in a way that couldn’t be solely attributed to a difference in digital signal input levels.

Now this could be due to any number of reasons, from difference in output levels, to the much shorter signal path or the fact that the two components have been extremely carefully matched and tweaked in the lab (rather than my front room) to achieve the desired sound quality. But the gap in sound quality is there, and it is noticeable.

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