John is quite correct to point out that in an LFR speaker system the DSP performs some essential functions that would otherwise be infeasible to implement. In contrast, these functions are not all needed in non-LFR systems and the only function that is provided by the DSP in such case has only a very subtle effect. Given that the added cost of the DSP is a fairly substantial sum it may be justifiable only to those most comcerned with achieving the absolute best possible sound.

Hi Chris (and Charles65),

I can happily (and will do so later today) post some graphs of our DSP box in straight "pass-thru" mode. Honestly, there will be nothing to see in the amplitude response curve until you approach the Nyquist Frequency (f_s/2) where there will be a steep roll-off. Distortion and noise are also of a magnitude below that of most amplifier stages.

I do understand the concern anytime something is inserted within the analogue signal path, and the timing of your posts is excellent as we are going to be embarking on a controlled test in late August that will be of interest to many of you. Basically will are going to setup a reference front end system comprising a calibrated open reel deck on which we will be playing 2 track mix-down master tapes. For many this is considered the absolute ultimate in purely analogue source material. The signal from this deck will pass directly to a Bryston pre-amplifier, or through our DSP box running in "pass-thru" mode. Because our DSP is unity gain no level matching will be required, and all switching is performed with high quality, silver contact signal relays. Listeners will be able to switch between the two signals at will and can listen via loudspeakers, headphones, or their own supplied headphone systems. We will have a Bryston headphone amplifier for headphone listening. Ian will supply the specific details as we nail down firm dates and have procured some master tapes, but this session will run for a number of weeks and be open to ANYONE that would like to make the trip here to participate.

The question of digital inputs, as Chris correctly points out, is fraught with problems and only removes the ADC component from the equation. Simply trying to determine all of the required inputs and format standards results in a device that would be riddled with inputs and additional cost, not to mention ever-changing formats and HDCP requirements. In that sense it makes much more sense for us to stay within the analogue chain.

Thank you John (and Andrew and Chris also) for all your (DSP box) explanations. I understand better what it does. You are all much more knowledgeable than me in electronics. But I would have to disagree that above a certain limit all electronics are equal (if I understood well what you are suggesting). They might measure the same, as Celine Dion singing a note at 400Hz will measure the same as Aretha Franklin singing a note at 400Hz but you will agree that it won't sound the same to your ears! I do not know if my analogy is valid here. I guess what I am saying is that I do not think measurement is an absolute criteria. Are you saying that as long as it measures the same, your ear could not make a difference and the only difference would be in someone's head? As a scientific (not in electronics obviously! ), I am very open to this argument but frankly It is very far from corresponding to my lifelong empirical observations. Note that I am not saying that the price is an absolute criteria either and there is a lot of charlatanism in electronics. But having listened to a lot of DACs (streamers, processors, simple DACs) it is impossible for me to say they all sounded the same. It would be like saying all apple varieties taste the same because they are apples after all. It is just not what the chemical reactions in my brain is telling me.

Your analogy is invalid, just FYI. It is impossible for a human to produce a tone that lacks overtones/harmonics, which is what make people singing the same note sound different.

Interesting, thank you. So what you are saying is that there would be a measure that could explain the differences between what we hear. But this measure would not be the note or the fundamental tone at 440Hz. Would there be measures that could explain the differences between DACs chips? Because when I look into the specs of Wolfson DAC chips for example http://www.wolfsonmicro.com/products/dacs/ ,
it seems to me that the differences in SNR ratio for example are quite substantial and possibly audible (i.e not all DAC will sound the same since I think that 20-30 dB differences should be easily audible to the ear no?).

If the SNR was 20 or 30 dB you'd be able to hear that, but the difference between 98 and 128 is meaningless. Because you can't hear noise that is 98 dB below the signal in the first place. In a very, very quiet room, you may be able to hear noise that is 84 dB (14 bit) below the signal.

Oh, and it's not a "measure" of what's different between two voices (be they human or instrumental) producing a sound with a fundamental frequency at 440 Hz. They are two completely different waveforms. It's only the slowest part of the waveform that's cycling at 440 times a second. That's what gives any instrument its unique timbre.

But it is possible to digitally capture and accurately reproduce any of those sounds that exist below the Nyquist of the sampling system.

Nice work, Chris.

No, Charles; the point is that the measurements won't be precisely the same when instruments far more sensitive than our ears are used, but we can be unable to distinguish these small differences in controlled listening tests.

Thanks to you all for those explanations. Still it does not explain why I sometimes hear so much differences between DAC's (and processors in general). And I am not talking about subtle differences. It is true that between some DAC's the differences are very subtle that it would be possible that I imagine some (différences). But in many many cases, the difference is so in my face that you would have to be deaf or hypnothize to not hear it. For example, with my old Cambridge DAC magic (which I think is an excellent DAC for the price), I could hear very remotley Cecilia Bartoli taking her breath in (it was like in the background somewhere). Now with my Linn Majik, it is like she is breathing in my face. You clearly hear her respiration. It is impossible to not hear the huge difference. In some other recording, I could hear clearly the skweaking of the pedal drum with one DAC and not at all with the other one. So my deduction is that if I can hear (and everyone in the room also) this pedal skeaking it must exist in the recording. And if a source is not able to reveal that from the recording (giving all other Equipment the same), what else it is not revealing....