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RE: The 4 ways to decode digital

Posted by Thorsten (M) on October 15, 2015 at 20:25:42

In Reply to: RE: The 4 ways to decode digital posted by J. Phelan on October 15, 2015 at 19:09:40:

Hi,

> I don't believe they are.

There is a difference between presenting the truth in an advantageous way and lying. But I suggest to look at the what is on the circuit boards... I love tearing down (and then re-assembling) competitors products. I'd love it even more if on occasion I'd learn something I don't know, I mean apart from another way to fluff things up.

> And saying that sampling in the mega-hertz is "too low" doesn't make
> sense to me.

You should read my old "Tubes for DAC's" article (Valve Magazine - Issue 2, 2000). I cover this stuff in some detail...

In order to make single bit ADC/DAC that has 16 Bit/44.1kHz equivalent resolution using a single bit system WITHOUT noise-shaping reqires 2.9GHz sample rate. Seriously.

So no matter what rate 1-Bit ADC's and DAC's (and a digital input Class D Amp is just a 1-Bit DAC and an analogue input Class D Amp is actually an ADC followed by a DAC) sample at, they are WAY TOO SLOW.

They "make up' this lack of sample rate by using noise shaping. We could now descend deeply into the details of that, but I'd rather listen to some music instead. Life's too short and all.

> Acoustic mikes can't capture above 25kHz.

I am not sure what you mean with "acoustic mikes". I have a mike here with 4939 written on it. I use it to measure speakers. It's an "acoustic microphone" and it is fine at 100khz.

> The type of music that audiophiles (largely) listen to. And how about
> vibration-induced noise ? Mikes have a S/N limit of 92.

Well, the 4939 has a self noise of 28dB (absolute) and can (in theory) handle 164dB... Bigger capsules have noise as low as 9dB. Something I personally might use to record comes in at 12dB.

Recording classical at around fifth row in the royal festival hall has 110dB peaks at fff. If you place the mikes where they usually are (above the conductors rostrum) add another 10dB. So that is around 108dB real dynamic range.

Of course, you could never release that sort of recording commercially, you will have to gain-ride (or if you are a dum-bass use electronic compressors) to compress these 108dB to less than 60dB.

Or if you are recording "popular music" it may have to be compressed to less than 10dB, to make it sound "loud".

> Even if (some) mikes can go to 100kHz, I wouldn't want to be around to
> hear the results...

The sense or lack thereof for ultrasonic sounds and system responses is debatable. But are you perchance familiar with the work done by Tsutomu Oohashi on the subject? Recommended.

Of course, in the end we are back at: "Go and listen and care less about the Tech, than the sound!".

Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

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