- Written by John E. Johnson, Jr.
- Published on 11 June 2009
On the Bench
In the 1 kHz and IMD tests, a 24 kHz bandwidth was used. For 10 kHz, bandwidth was 96 kHz. Test signals were recorded at - 5 dB. I used one of the DacMagic's XLR outputs connected to the analyzer. The DacMagic outputs quite a bit of voltage, and when the Squeezebox was turned up to full ouput, I only had the lower 20% of the BAT volume control to work with, because any higher than that was too loud for me. So, I set the Squeezebox volume control at about 75%, which I suspect most consumers might want to use as well because it gives you more room in the preamplifier volume control.
At 1 kHz, THD+N was 0.003%.
At 10 kHz, distortion rose to 0.006%. There are three 10 kHz graphs shown below. The first one was taken in the Linear mode, the second in Min mode, and the third in Steep mode. There are subtle differences above the audible band, but the overall distortion was about the same for all three filters. The hump at 80 kHz is the quantization noise that results from using Delta-Sigma (1 bit) DAC chips. The bits are modulated such that the noise is pushed far out of the audible band. As a side note, SACD is also a 1 bit decoding process, so it also has a hump outside the audible band.
IMD was 0.0025%.
The measured frequency response of the DacMagic was 20 Hz - 20 kHz, - 0.3 dB at 20 Hz and at 20 kHz. For the Squeezebox, the frequency response was 20 Hz – 20 kHz, - 0.7 dB at 20 Hz, and – 0.5 dB at 20 kHz.
So, now let's compare the DacMagic to the Squeezebox. I connected one of the RCA analog outputs from the Squeezebox to the analyzer. The volume control on the Squeezebox was left at 75%.
At 1 kHz, distortion was 0.02%, more than an order of magnitude higher than with the DacMagic.
At 10 kHz, THD+N was 0.05%, again, much higher than with the DacMagic.
IMD was about twice what it was with the DacMagic.
I also measured the Squeezebox at just under 100% output to see if distortion improved.
At 1 kHz, THD+N was 0.007%, improved from the 75% output, but still twice what it was with the DacMagic at 75% output.
At 10 kHz, distortion was a still a full order of magnitude larger than the DacMagic, in fact, a bit more than it was at 75% output.
Squeezebox IMD at full output was just a bit less than it was at 75% output, but still more than the DacMagic.