While this technical description sounds promising, one key question remains: why go with a DSD-centric DAC in the first place? The answer is a multi-faceted one, but let me attempt, here, to synopsise a mini-White Paper PS Audio has provided on the subject. The designers chose DSD as the core platform for this DAC with several thoughts in mind. First, DSD is simple to convert to analogue, requiring only a low-pass filter. Second, DSD is inherently linear and all bits in a DSD stream have the same weight, meaning, says PS Audio’s White Paper, “a single-bit error anywhere is barely measurable let alone audible” (something that is not always true with conventional PCM playback). Third, DSD soft clips when overdriven, meaning that a DSD-based DAC should theoretically behave more like analogue magnetic tape, where “signals which exceed the nominal full scale value only get slightly compressed if at all.”
The DirectStream DAC provides a card slot for an optional Network Bridge module, plus a range of digital inputs including AES/EBU (via XLR), coaxial and TOSlink S/PDIF, I2S, and USB. Two methods of control are provided: a full-colour touchscreen display and a convenient, handheld remote. Many different display views are possible, but the standard one shows the DAC input selected, the sampling rate and bit-depth of the file in play, and the absolute phase setting chosen (the DirectStream DAC allows switching of absolute phase, which makes a significant difference on some recordings).
If the optional Network Bridge is installed, the DirectStream DAC will automatically access the Internet to look up album art and metadata for the files being played and then store that data on an included SD memory card. Thereafter, the display will show the appropriate album art and metadata whenever the file is played. The display screen also will temporarily show volume and/or channel balance settings whenever users adjust either parameter. Although the DAC can be set to provide fixed, line-level outputs, PS Audio strongly recommends using the DAC’s variable level analogue outputs (either balanced or single-ended) to drive power amplifiers directly, arguing that there is nothing quite like the sonic transparency and purity that results. Consequently, I ran the DAC directly into my reference monoblock amps.
According to its specifications, the DirectStream DAC can handle PCM files at up to 192kHz/24-bit resolutions, but I got a pleasant surprise when I discovered the DAC could happily play the 352.8kHz/24-bit DXD files I had on hand (and it sounded terrific doing so!). The DAC also is rated to handle DSD64 and DSD128 files, which it does with the greatest of ease (but note: it cannot play ‘quad speed’ DSD256 files).
In the title of this article, I mentioned that our review sample of the DirectStream DAC had PS Audio’s latest Pikes Peak ‘OS’ or ‘operating system’ installed. I used that phrasing because PS Audio describes its elaborate control firmware for this DAC as being not unlike a full-fledged computer operating system, owing to the extreme volume and complexity of the code involved. To date, there have been three operating system updates for the DAC – all free of charge – and according to Paul McGowan (and others in the PS Audio user community), the Pikes Peak OS represents a bigger sonic step forward than any of the previous upgrades.