New Firmware: Measurements

Firmware v.1.2.1 Measurements, from March 2015 (Vol.38 No.3)

Art Dudley received the v.1.1.4 firmware upgrade for PS Audio's PerfectWave DirectStream ($5999) toward the end of his time with this superb-sounding, DSD-capable D/A processor, so was able to write only a brief report on the change this made to the review sample's sound. "For those who've waited for a computer-friendly DAC that offers, with every type of music file, the best musicality of which DSD is capable, the PerfectWave DirectStream may be in a class by itself," he concluded. In my own auditioning of the PS Audio with the v.1.1.4 firmware, I was also impressed by its sound, feeling it had a smooth quality that made the otherwise excellent-sounding Luxman DA-06 D/A processor ($4990), which AD reviewed in July 2014, sound a touch too immediate in direct comparisons.

However, my measurements had revealed some problems in the PS Audio DAC, even with what was then the latest version of the firmware. In particular, I was bothered by the DirectStream's ultimate lack of resolution with data capable of higher-than-CD resolution, and by the poor linearity at low frequencies. When I discussed these issues with PS Audio's Ted Smith and Paul McGowan last October, at the 2014 Rocky Mountain Audio Fest, they told me that because the DirectStream's data processing is performed by Field-Programmable Gate Arrays (FPGAs) rather than by dedicated chips, these problems could be addressed with a firmware upgrade. That update, v.1.2.1, was already available for download before RMAF (footnote 1) and as Robert Deutsch had just purchased a DirectStream DAC, I asked him to write a Follow-Up comparing the sounds of v.1.1.4 and v.1.2.1. That enthusiastic Follow-Up appeared in our February 2015 issue (p.129); meanwhile, as I still had the original review sample, I upgraded its firmware and got it up on my test bench.

As always, I performed the tests with my Audio Precision SYS2722 system (see the January 2008 "As We See It"), which had just been returned from Audio Precision for service and recalibration. As before, all the measurements were performed from the processor's balanced outputs with the volume control set to its maximum.

Fig.1 PS Audio DirectStream, v.1.1.4 firmware, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with 24-bit data (left channel blue, right red; 5dB/vertical div.).

Fig.2 PS Audio DirectStream, v.1.2.1 firmware, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with 24-bit data (left channel blue, right red; 5dB/vertical div.).

Fig.1 shows the spectrum of the DirectStream with v.1.1.4 firmware while it decoded 24-bit data representing a dithered 1kHz tone at –90dBFS, plotted from –60dBFS downward. Fig.2 shows the spectrum with the v.1.2.1 firmware. You can see that both the noise floor and the already low-level power-supply products at the left of fig.1 have dropped by 3–5dB with the new firmware.

Fig.3 PS Audio DirectStream, v.1.1.4 firmware, spectrum with noise and spuriae of dithered 1kHz tone at –120dBFS with 24-bit data (left channel blue, right red; 5dB/vertical div.).

Fig.4 PS Audio DirectStream, v.1.2.1 firmware, spectrum with noise and spuriae of dithered 1kHz tone at –120dBFS with 24-bit data (left channel blue, right red; 5dB/vertical div.).

Perhaps more important, figs. 3 and 4 compare the PS Audio's reproduction of a dithered 1kHz tone at –120dBFS with the old and new firmware. With v.1.1.4, the fundamental tone was suppressed by 5dB, and it was the second harmonic that peaked at –120dBFS. With v.1.2.1, the 1kHz tone peaks at the correct level, which suggests a significant improvement in low-level linearity.

Fig.5 PS Audio DirectStream, v.1.1.4 firmware, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

Fig.6 PS Audio DirectStream, v.1.2.1 firmware, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

Figs. 5 and 6 similarly compare the spectra of the DirectStream's output while it drives a full-scale 50Hz tone into 100k ohms with the two firmware versions. With v.1.1.4 (fig.5), the second harmonic reaches a high –43dB (0.7%) and the third harmonic –52dB (0.2%). By contrast, with v.1.2.1 (fig.6), both harmonics have dropped to –60dB (0.1%) or below, and the higher-order harmonics visible in fig.5 are also much lower in level. While the v.1.1.4 version's linearity was better at high frequencies than at low frequencies, v.1.2.1 was even better.

Fig.7 PS Audio DirectStream, v.1.2.1 firmware, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).

The spectra of the upgraded PS Audio's output while it decoded an equal mix of 19 and 20kHz tones (fig.7) revealed that the difference tone at 1kHz had dropped by more than 10dB, to –90dB (0.003%), and that the noise floor was cleaner than it had been with the earlier firmware.

The measured reduction in low-frequency distortion with the v.1.2.1 firmware is dramatic, the improvement in resolution less so but still worthwhile. Kudos to PS Audio for designing a product so that its performance can so easily be upgraded by its customers. The new firmware is a gift to end users that will keep on giving.—John Atkinson


Footnote 1: See Paul McGowan's and Ted Smith's comments on the reasons for the upgrade, as well as reactions from owners, here.

COMMENTS
jazzbirder's picture

I am having some problems with the new P S Audio DirectStream DAC I bought. I am not a audiophile or a computer wiz. I have an old Dell from 2004. I called P S Audio to help with downloading the software and fired up the DAC. Using my USB cable, I was able to listen to WBGO on the net, but I could not listen to WKCR because Windows Player and Real Player gave me error messages ! I need someone who knows audio and PCs !

John Atkinson's picture
jazzbirder wrote:
Using my USB cable, I was able to listen to WBGO on the net, but I could not listen to WKCR because Windows Player and Real Player gave me error messages!

As you were able to listen to WBGO via your Internet connection and the PS Audio DAC, this suggests your set-up is correct. If you set the PS Audio via USB as your PC's default sound device, are you able to listen to things like YouTube using your Web browser?

John Atkinson
Editor, Stereophile

John Atkinson's picture
dcolak wrote:
https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-ps-audio-perfectwave-directstream-dac.9100/

Thank you for the link. Amir's measurements aren't that different from Stereophile's, so I am not sure why you imply ours aren't "real."

In addition, when he quotes me as saying in our review that "In many ways PS Audio's DirectStream DAC measures superbly well but..." and says "What? Superbly well? This is is superbly well?" and shows the poor low-frequency linearity graph from my measurements of the review sample with the original firmware, he is ignoring both my "but" and the subsequent measurements at www.stereophile.com/content/new-firmware-measurements, which show that this poor performance had been addressed.

John Atkinson
Technical Editor, Stereophile

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