PS Audio DirectStream DAC measurements by ASR


From one of the more useful comments on the PSA site (I do think that thread was worth reading.  In terms of context, it appears most of the response to the review is that the measurements are mostly "bad" because of the DSD's high noise floor, which is an inherent part of the design.


"tarnishedears:  One of the key design goals of the DS was to create a “DAC” which did not contain any sort of “DAC” per say, but instead it just passively converted a DSD stream to analog using a simple low pass filter. Unfortunately this approach necessarily will have a higher noise floor than will most other approaches.

This is one design goal which the DS DAC shares with some of the Lampazator DACs. The fundamental difference between a DS and (some of the) Lamps is that the Lamp essentially just takes an input DSD stream, and it low-pass filters it (turning it into analog) and then it buffers/amplifies this output using tube output stage.

The DS on the other hand takes all input signals, up-samples the input to 20x DSD and then passively low-pass filters the output, thereby transforming it into analog. But instead of using a tube output stage like the Lamp, the DS Sr uses a 100% passive low-pass filter stage with incorporates an output transformer as the buffer, and as a key part of its filter network.

This is largely a simplified version of same the basic design which Ted’s legendary prototype DAC used (although the firmware on the DS is much more refined now). This is the DAC which he originally pitched to PS Audio. And it is, by all accounts, supposed to be the very best sounding DAC that anyone who has heard it has ever heard.

Part of the magic of this design is that it performs a 100% passive conversion of the digital signal to analog. This is, in fact, what the “Direct Stream” in the name is all about. To not convert to analog this way is to have a DAC which isn’t a Direct Stream DAC. Unfortunately the price for this particular very deliberate engineering design decision is always going to be a higher noise floor.

But unless you are running this DAC straight into your power amp (which I do not recommend) , what does this even matter? This DAC is still just as quiet as was an older CD player containing an 18 bit DAC. And nobody ever complained about those players being too noisy back then, did they? In fact, Amir’s so-called objectivist press would-be peers of time in magazines like Stereo Review were fixated on even the worst CD players of the time having “perfect” sound. To them and that the newer generation of players which incorporated 18 bit DACs were completely unnecessary from their point of view because even the worst players measured “good enough” to them. So which way is it? Does any DAC with less than a theoretical 24 bit noise floor now suck, or was the 16 bit noise floor of a early CD players more than adequate as was claimed as the time? This is a fundamental contradiction which his work would seem to have with the claims which were made by many of the members of yesterday;s objectivist community.

Noise floor does not equal resolution. This is one of the areas where Amir and many of todays objectivist go wrong. Higher resolution is a requirement to have a lower noise floor, but the opposite is not necessarily true as signals can still exist well below the noise floor.

And the DS is still much quieter than any type of analog source, even when using noise reduction. And yet I don’t hear very many audiophiles claiming that 15 ips R2R sounds bad, or that a really quiet LP is way too noisy. Although perhaps Amir very well might maintain such a position? But since I don’t waste my time by closely following his work, I wouldn’t actually know."

The answers to this thread for sure will reassure PS.

No matter that its DAC is introducing harmonics where they don’t exist, that is changing the original music and removing any hope of fidelity. The denial bias of many people confronted with proofs will save their business.
Results from the measurements are obvious: there are $100 DACs with much higher fidelity than the PS Audio DirectStream.

 After these measurements they played the same silly PS arguments to save their face, but at the end they learned the lesson and now they produce acceptable gear. It’s likely that PS will do the same, as they are clever business guys.

The basic task of a DAC is to recreate the digital signal without noise. A 6k device is failing in basic measurement. Will you be happy with a car which is advertised at making 400HP making 130HP on dyno?
Well, actually the measurements made by Amir exceed the specs published by PS Audio. 
Well...I would have to think that anyone who spent hard earned cash on the DS dac must be "stone cold deaf". After all..we all know that measurements in the audiophile community always trump ones own personal preference when it comes to quality of sound... 8)