You need to invite a bat over to your house to listen to a DXD recording of Johann Strauss II – Die Fledermaus (The Bat, although it is sometimes called The Revenge of the Bat) to assess your system’s quality. As far as I know, the only high-resolution recording is Lawrence Foster and the NDR Radiophilharmonie at 96k samples/sec so the bat will complain of a missing high end. Note only a small 2nd harmonic distortion product at -135dB and no hum components at all. How is that possible? This test is all done on batteries. The Topping D10 is USB powered and so is the Quantasylum QA401. I drove the Topping with a Lenovo E595 and the Quantasylum was on a Lenovo T560. Why am I mentioning Lenovo? Other computers may have noisy USB power outputs and you will not get these results. Since I did not stream music in the past, I had no need for a USB DAC. I would connect my hard drive with music files to an audio component that can decode them directly and send them via HDMI to my AVR with room correction. The little Sony BDPS6700 BluRay player I reviewed does that. The chip is screened by an unusual ferrite 'gate' - this is the first time I see such an arrangement in any hifi product. The 'gate' forms a 'ring' that screens the chip 360' (over and below the PCB): All those years I waited---companies were working feverishly to improve the sound you get from taking USB and extracting audio data out of all the streams that are coming out of USB simultaneously.

You can see it is flat past 85kHz. Some of the roll-off above 85kHz is the ADC in the QA401 spectrum analyzer which is also running at 192k samples/sec. Since I can only sample at 192k samples/sec maximum with the QA401 I could not observe the stopband. Any doubt about the Windows 10 driver being high resolution is dispelled by the result above coupled with the measurements that preceded this. Moving the test frequency to 10kHz (not shown) the Topping D10 2nd harmonic was at -116dB (0.00016%), and the D10 hardly moved to -115dB at 96k samples/sec and -114dB at 192k samples sec. Harmonics beyond the 2nd were not observable with the spectrum analyzer at 48k samples/sec sampling rate. The QA401 performs better at the lower sampling rate which is a USB powered ADC limitation. Also, note the noise is up as a result of the QA401s 20dB attenuator in the signal path. The QA401 ADC distortion degrades if the signal is above 200mvRMS so I traded noise for distortion accuracy by using the attenuator. Note the Windows 10 High-Resolution Driver up-samples. If you select 384k samples/sec that is what the Windows driver will put out and that is what the Topping front panel will show. In this case, Windows is up-sampling to 384k samples/sec regardless of what the file sampling rate is. Up-sampling does nothing for the sound and introduces unnecessary signal processing. You are not getting a bit-perfect representation of the file at the USB output. The DAC is getting pushed to its maximum rate for no reason and this reduces performance.I did not take the box apart, but you can see the internals on the internet if you look for images of the Topping D10. After a cursory survey of the different adapters concerned, I was immediately drawn to this unusual audio piece. It is literally a cable, with the electronics built into the cable – the S/PDIF end. It takes it’s power from the USB on the laptop, but can be cleverly upgraded by providing dedicated power.

I am showing only one channel so you can see the analyzer’s residual noise floor, with a shorted input, but both channels of the D10 produced the same results. Words are one thing, data is another. So let's see measure the performance of S/PDIF and DAC on the same USB and see how they differ. Alas, USB seems to have taken the market by the storm and increasingly DACs have only USB input. I had to dig deep in my stash of DACs to find the ones that still have S/PDIF input. Here is their performance on the venerable J-Test signal at 48 Khz/24-bit. To me Berkeley Audio Designs Alpha USB defines the current state of the art in USB/SPDIF converters design. Here is a 40 kHz tone sampled at 96k samples/sec rate. The level is 0dB. This time I used the Flat Top window to get the best estimate of the gain of the signal. This is a 0dBFS tone. Note the X-axis of the graph is dBr with 0dBr at 2VRMS.

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KLIPSCH MICROTRACTRIX HORN TECHNOLOGY makes a major contribution to the ProMedia’s amazing clarity. Their highly efficient design reproduces more sound from every watt of power, controlling the dispersion of that sound and sending it straight to your ears The QA401 analysis software is close to AP quality including SNR in the presence of a test tone that is not even available on the older Audio Precision Analyzer that Secrets owns. It is on the latest Audio Precision units. The QA401 is smart enough to identify harmonics from the test tone and does not use those FFT bins in the SNR computation. SNR can drop when a signal is present which is why this readout is so important.