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Doing some further thinking by my mind that has “little understanding about the technology” I would like to share another concern that for my little mind does make since.

According to Mr. Donahue comments above playing the BSO files with a possessor that has HDCD decoding activated provide a “significant increase in the spatial imaging and overall imaging acuity” as the activation of HDCD decoding will inform the “DA converter that the material was created  with an AD converter with a known anti-aliasing filter and noise shaping curve”. OK, I can’t corroborate on it now, Mani keeps silence about the validity of this claim (most likely he just has no options tot shut down the HDCD decoding as most of the DACs has no such a manual switch). I do not believe that what Mark Donahue suggest is not true. Most likely it is what it is, but if it is so then… I do not like it. Let me to explain.

Let pretend that we have an objective to deliver to the end user the SoundMirror’s BSO file at the best possible condition in term sound quality. If the configuration and type of the filters that prevents frequency sampled at higher than one-half the sample rate (aliasing) so affective to sound (wish it true) then let see what filter might be the most optimum for us?

Mark Donahue went for the filters that were used by Pacific in their HDCD. I have no knowledge what kind filters they used in there BUT the HDCD was designed and was beneficial ONLY at 44.1KHz format. So, regardless what they did in there the signal had to be stopped at 22KHz with the brick-wall effect. Yes, the Pacific is very good 44KHz DAC…. BUT the SoundMirror’s BSO file is not 44KHz files and this set all bid off.

This is just a brainstorming of the concept, and if Mark or others read it then do not be damn to recognize it as criticism but rather as collaboration how to get best possible results. What I question: if the selection of the 44KHz-targeted brick-wall filter is rational for 88kHz files. People go for sharp and complex filters at 44KHz as the Nyquist point is right there, very close to the upper edge of signal. With the 88kHz we care less about it as the Nyquist point is very far and we can go away with much softer filter and with much more phase-friendly curve. This absolutely certainly would NOT be a filtration that was meant for strictly 44KHz operation.

Now, we all know that anti-aliasing filters in many ways have negative effect to sound. But remember: our abstract objective is to have the best sound on the user side. So, what SoundMirror do? They select the configuration where the best Sound will be under a condition when s user engages the anti-aliasing filters designed for 44KHz HDCD. Leaving aside the fact that there are not a lot of HDCD DACs out there let ask ourselves if it was the best solution for BSO 88kHz files? My answer is that it was not. I think the best would be if SoundMirror folks use not the 44KHz HDCD filters for their reference but rather the 88kHz with no filters at all.

Sound damn, isn’t it? Well not necessarily. I think that amount of users out there who would be able to take advantage of HDCD filters is no higher than the amount of people who would be able to play the files with no filter at all. The advantage of playing the 88kHz files with no post-conversion filtration of any kind enormous theoretically and practically. Why SoundMirror folks did not go there? Well, because SoundMirror is a part of industry establishment and they need to embrace all industry rules of the game, no matter how stupid the rules are. However, in the case the BSO files the SoundMirror own the rules, why wouldn’t they get for the best the best?

To get the best it would need very little: the SoundMirror need to use for this reference while they master the BSO files a R2R Multibit DAC with no post D/A filtration of ANY kind. The true Multibit has no wide- bandwidth noise, the signal is fully reconstructed and there is no need for noise-shaping. Averything is already there, just buffering the signal and feed it to amps - and you have the rawest possible, virgin signal not contaminated by phase anomalies of any filtration – it imposable to have anything better than this.  Talking about “imaging”, that is a manifestation of phase consistency…

Sure you will have remains of the 88kHz sampling rate right along with you signal, so what? When did you hear the 88kHz last time? There is however a reason why SoundMirror would not go there, the industry things… Take a look at the SoundMirror control mastering rooms:

• The monitors are B&W Matrix series powered by Threshold amplifiers.
• Dunlavy SC series speakers powered by Classe amplifiers
• B&W Diamond series monitors powered by B&W amplifiers.

Is any pattern that you recognize in there? Yes, there one: all amplification that SoundMirror uses is push-pull, solid-state, high power amplification that most likely uses feedback, a lot of feedback. Those amps would NOT be very friendlily with high content of HF power in input signal and they very much might go berserk, oscillating, burn tweeters and do other nasty things. However, a good no-feedback amp with reasonable amount of open-loop equalization as well as any no-fedback SET users have would do perfectly fine with unfiltered Multibit output and will not have ANY of negative effect from the absence of post-conversion filters. I wish SoundMirror use THAT as the reference not the filters that were constructed for 16 bit 44kHz. The HDCD was wonderful under the umbrella of 16bit Red Book CDs. Now we are way beyond it and I think the SoundMirror with their 88kHz files might move forward along with the opportunities the new format implies.

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