Separation, output & noise

CD separation values usually exceed 100dB. Cambridge DacMagic shown here measures -137dB at 1kHz.

WHAT IT TELLS US

Separation between channels with CD, SACD and Blu-ray is, in a majority of players, very high, measuring around 120dB at 1kHz and 95dB at 10kHz. So there is little leakage of signal from one channel into the other, at least when one channel is muted. We measure separation to check that a player performs as expected here.

Output from CD players is set to 2V, but can be 4V from balanced XLR connectors.

Output was set at 2V maximum for CD, in Philips original Red Book standard. That means a -60dB signal outputs at 2mV and a -90dB signal at just 63µV – above noise but only just. All silver discs players nominally produce 2V maximum, although a tad more – around 2.6V – is quite common and some players double the figure through balanced XLR outputs. We measure all outputs, unbalanced and balanced.

Noise (unweighted) from a Cambridge DacMagic with input set to digital zero.

Noise measurement from CD is made uncertain by the common presence of zero level output muting in players. Those that mute return a -120dB noise value, but a true noise level of around -96dB can be expected when muting does not take place. So the large difference is noise between players has little to do with their true performance.

HOW WE MEASURE IT

We measure Separation at a player’s output terminals, using a spectrum analyser to eliminate the influence of noise and distortion. With CD and SACD players we use Philips SBC429 test disc. With Blu-ray players we use Rohde & Schwarz test discs from Burosch.

With DACs we use the digital signal generator within our Rohde & Schwarz UPL analyser to generate a 0dB, 1kHz tone on one channel and digital zero on the other.

Output is measured in volts out when playing full level 0dB on a test disc.

All our noise measurements are IEC A weighted and use maximum player output as the 0dB reference.