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There was some talk in another thread about MiniDisc.org and the fact that, amazing though it is, it hasn't been updated in a long time and many of the links etc are dead. This reminded me of something I had seen over on r/minidisc on Reddit about a new MiniDisc.wiki site.

The person who set it up posted about it HERE

The wiki itself can be found HERE

It's pretty sparse at the moment tbh but could well be worth keeping an eye on and, being a wiki, it's editable.

Anyone else noticed its existence?

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I just had a look. Bumped on some wild-ass discussion about "wide bit stream" and 24-bit DACs where most contributors are just shooting in the dark. Not the wrong end of the stick, the wrong forest.

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Ah, I’d noticed a lot of the contributions on the r/minidisc Reddit were, err, somewhat less knowledgeable than you get on here (not including myself in that - I’m fairly clueless) but the couple of pages I’d looked at on the Wiki just seemed to be fairly basic information about particular devices. 
Oh well. 

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Ah, I think you were reading a discussion on Reddit, rather than the wiki?

The Reddit discussions are often full of nonsense, sadly. You do occasionally get some nice pictures of people’s kit though :-)

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If the stated intentions can be achieved - i.e. a robust long-term archive of the valuable technical and machine documents then I think it's a worthy exercise. If it's a Twitter for the airing of random misnomers about the technical details then it's just a gossip site. We currently have here, Tapeheads plus .org. Whilst we're all on a voyage of discovery and none of us were actually on the Sony design teams, I don't think as yet either existing forum has degraded into one of arbitrary clueless contribution. At least on here I think we own up when we get to the limits of our knowledge. That's not to say we don't push the boundaries of our learning, but I don't think we make a habit of claiming knowledge where we have none.

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3 minutes ago, BearBoy said:

Ah, I think you were reading a discussion on Reddit, rather than the wiki?

The Reddit discussions are often full of nonsense, sadly. You do occasionally get some nice pictures of people’s kit though :-)

I'll add myself to the list. I've just clearly demonstrated I'm no wiser. Or at least I'm incapable of navigating a website.

I'll say that's a software problem not a hardware one.

I'll get my coat.

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This is a beautiful interview, if you can drag your way through the translation. You can feel the Sony engineers battling to get the concepts across to the interviewer who is hell-bent on reducing the discussion to "my (digital) bits are better than your (digital) bits". ATRAC is far cleverer than that. It's Adaptive, it's in the name. Nothing is fixed. It can "mould" itself to the music to capture what is needed to reproduce it most accurately. The ATRAC encoder is a thing of mathematical beauty and that Sony were able to implement such mathematical complexity in electronics for a consumer product in <1992 is frankly astonishing.

http://minidisc.org/mj_ja3es.html

Also recently I've been reading on here some mention of "fixed" and "floating" in the context of "fixed point" and "floating point" (terms we would traditionally associate with IEEE 754). "Floating" in the MD world is somewhat different (although you could loosely relate SF to exponent). This is covered quite nicely here in Figure 5, then related to Scale Factor in Figure 4.

As I whined about the reddit thread above I'll also note that in respect of the 24-bit ADCs, the ADC generates the samples in the <time domain> whereas the "throwing away" that ATRAC does for compression is in the <frequency domain> (after the Fast Fourier Transforms the CXD DSP does). This key point is thoroughly lost on the contributors on that reddit thread. They were going on as if the "throwing away" was discarding samples and/or ADC bits in the time domain. Wrong...

One other point, as I've just been looking at related websites that talk about digital sampling in an ADC. Some of their diagrams are very misleading. Can I state here and now, that as long as an ADC samples a bandwidth-limited signal at at least twice the highest required frequency, then the DAC will reproduce the analogue signal perfectly. Even if that ADC was just a few bits. The number of bits of an ADC does not affect the quality of the waveshape once reproduced (number of bit affects the dynamic range and noise floor). Just because you sample and quantise a real-world analogue signal at discrete time intervals to discrete quantisation steps (i.e. integers), you do not get back out a steppy rough analogue signal (like some of the diagrams I have seen suggest). If you put a perfect 20kHz sine wave into an ADC sampling at greater than 40kHz, this sine wave will be reproduced perfectly and smoothly once you have passed that discrete digital sample set back out through the DAC and LPF.

OK I'll stop ranting now (maybe).

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The comparison to DAT in that interview is interesting. I'd always been led to believe that DAT was a superior system (sound quality wise, not from a functional perspective) to MiniDisc due to the latter's compression. Seems like things are far from that simple.

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34 minutes ago, BearBoy said:

Seems like things are far from that simple.

Indeed. DAT like CD is 16 bits. Forever.

MD may well have started as 16 bit (because it was restricted by the processing power you could put on a consumer chip in the 1990's), but if you can get the ADC/DAC and have the number crunching power in your DSP to do the FFTs/IFFTs to convert the samples to/from the frequency domain then 18 or 20 bit resolution is achievable with the format. Note: 16 bits to 20 bit is absolutely massive in dynamic range/noise terms. Don't let those little 2- or 4-bit increments fool you - it's not a change of "2" from 16 to 18, it's 4-times and 16 to 20 is 16-times - repeat 16 times the dynamic range. This can be seen with the increasing dynamic range specs as ATRAC evolved[*] (expressed in dB - a logarithmic, not a linear scale). Beyond 20 bit, you're not designing for the human ear, because even 16 bit dynamic range is pretty much at the practical ear/brain limit anyway. That's not to say you wouldn't want more "bits" in the audio chain that's being used to generate the content, i.e. the recording studio, because as you combine and mix the tracks you want to be able to deliver a final master "tape" that can achieve 16 bit dynamic range (i.e. the noise floor is still at least 16 bits, not degraded below).

I will (try and) stop now, because I admit I will start getting out of my depth with the maths...

[*] Note within product families the improved dynamic range specs are due to better (more expensive) ADCs, DACs, better quality (electrically less noisy) power supplies and better filter components in the higher spec machines - the 9xx compared to the 5xx etc.

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