Quote Originally Posted by RGA View Post
Feanor

I won't disagree with you on the seeming snake oil commentary. If I read before I heard I'd say the same thing - oh wait - I did back when I was about to buy a B&W and Bryston system - as those pieces are certainly "safe" with lots of numbers on their side. Peter puts out a lot of layman talk I suspect because that's easier for him to get his head around it - perhaps what he should do is let his engineers do the talking for engineer readers. Most aren't however. Andy Grove on their Digital technology Audio Note Kits - Why is AudioNote's 1X oversampling unique?
This is old stuff, but one must grant that Andy Grove comes away sounding more rational then Qvortrup.

Still you get this: "When a set of samples is passed through a digital filter, what you get out won’t be an interpolated superset of the input samples, which is the fundamental premise of the whole technology, they will be an entirely new set of samples.

Therefore philosophically there is something wrong with digital filtering and this is proven in practical listening tests. Hence we do not oversample the input signal or digitally tamper with it at all."

To paraphrase Goering, when I hear "philosophical" in at technical context, I reach for my gun.

Of course it's true that frequencies coming out to DAC that are above half the sampling frequency, (i.e. 22 kHz in case of CD), are noise. This garbage is potentially damaging to amplifier circuits and speakers.

It's also true that steep analog filters cause phase shifts in the audible range, and it's true that the most often used digital filter, (FIR = finite impulse response), is phase linear but causes the "pre-echo" that Groves describes. Two things can be said about that: (a) it's not clear that the "pre-echo" is actually audible, and (b) in any case, other digital filtering options are available, e.g. in case of the Cambridge Dacmagic where the type of filter is selectable.

The Grove/Qvortrup solution is to not filter at all (!!). Instead they rely on non-linear components, viz. transformers and tubes, to filter out the HF garbage. This is yet another example of Audio Note ignoring best practice; John Atkinson always expresses a negative comment when he reviews a non-oversampling or non-filtering DAC.