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Old 14th February 2020, 06:39 PM   #91
scott wurcer is offline scott wurcer  United States
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Originally Posted by marklawrence View Post
We had recorded some live music at 18 bits 50khz. I was not present for the recording. The music was stored on, as I recall (remember, this was 40 years ago), a PDP-10 where we could do all the DSP we wanted. The project was in Pasadena, everyone there was a Caltech grad or student. I was a senior.
Mark did you know James Boyk, I took my daughter to visit Cal Tech when she was interviewing colleges and got a very sad message on his answering machine that his position was eliminated. I really wanted to meet him.
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Old 14th February 2020, 06:55 PM   #92
marklawrence is offline marklawrence  United States
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I didn't know him personally, but I heard him perform a couple times. He was superb.

Before that we had a poet in residence who wrote this:

At the California Institute of Technology
BY RICHARD BRAUTIGAN

I don’t care how God-damn smart
these guys are: I’m bored.

It’s been raining like hell all day long
and there’s nothing to do.
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Old 14th February 2020, 08:15 PM   #93
scott wurcer is offline scott wurcer  United States
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At the California Institute of Technology
BY RICHARD BRAUTIGAN
He has a special place for me, I took an incomplete in a humanities course and two years later read "In Watermelon Sugar" and sent a fairly incoherent assessment of it to the teacher who had moved to SUNY. She sent in a grade so I could secure my escape from MIT.
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Old 14th February 2020, 09:05 PM   #94
audioaficionado is offline audioaficionado  United States
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Thanx to all. Very interesting info and viewpoints. I think I've found the best bang for the buck solution. Rega Fono Mini A2D ~$160. Great sound, specs, price and does 16-bit/48 kHz ADC using Audacity. I can't hear past 10 kHz and it's only getting harder as the years march on.

Oh... and my cats always get all the sweet spots
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Last edited by audioaficionado; 14th February 2020 at 09:08 PM.
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Old 14th February 2020, 09:31 PM   #95
scottjoplin is offline scottjoplin  Wales
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I can't hear past 10 kHz and it's only getting harder as the years march on.
I'm not convinced recorded bandwidth is only to do with limits of higher frequency hearing ability.
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Old 15th February 2020, 12:02 AM   #96
stocktrader200 is offline stocktrader200  Canada
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marklawrence , thanks for the knowledgeable response. great explanation.
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Old 15th February 2020, 07:50 AM   #97
jaddie is offline jaddie
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Originally Posted by marklawrence View Post
We had recorded some live music at 18 bits 50khz. I was not present for the recording. The music was stored on, as I recall (remember, this was 40 years ago), a PDP-10 where we could do all the DSP we wanted. The project was in Pasadena, everyone there was a Caltech grad or student. I was a senior. We were using, of course, all Pioneer equipment - their top of the line speakers and electronics, which were not so bad. We down sampled the music to various formats, including 16/50 and 12fp/50. None of the tests were double blind, we were investigating and convincing ourselves, not trying to prove anything. The 16 and 12fp sounded about the same. The 18 was slightly better. I repeated the tests on my home stereo - Tympani IIIs, Ampzilla 500 / Marantz DC 300, home made preamp. The DC 300 was modified by me, the Marantz designers had made a beginners mistake in the current amp section which I fixed, lowering the crossover distortion from slight to negligible. The preamp was 356s for the high end signal, 318/394 phono preamp. I would use different stuff today, but at the time it was as good as anything out there, and the phono preamp was better than anything else out there.

It's worth remembering how this format got started. 16 bits because that was the realistic limit for finite dollar ADC converters at the time. Actual CD players at the time frequently had 12 bit DACs and sounded horrible. 16 bits also because it was a computer word - 2 bytes. Recording formats - CDs - were chosen to hold just over an hour of music, 'cause they had to hold the 9th. This was the actual spec, CDs had to hold the 9th. 44.056khz 'cause that could be done and allow the CDs to play for 65min. Doesn't it seem rather lucky that today, when we can easily do 24 bits at 200+khz, that a 2 byte computer word at a sample frequency >40khz but could fit 65min in a CD would turn out to be exactly optimal? Not 15 bits, not 17 bits, but 16 exactly? Doesn't that seem a rather unlikely coincidence?

The best fit to the observed hydrogen / helium ratio of the universe is for 3.4 families of elementary particles. But you can't have .4 of an electron, so the actual universe has 3 families, electron, muon, taon. What's the actual optimal number of bits for audio? To my knowledge, that number has never been calculated. Audio engineers aren't typically that good at math, and it's doubtful the test data for human hearing is good enough to support the analysis. BTW, your human hearing charts looked just like that in the 70s, I question their accuracy. It would be nice is someone redid them with better equipment and better procedures. Unfortunately, as we all know, stereo is all but dead. It's all MP3 or youtube or home theater now. I'm really quite stunned that so many speaker manufacturers have survived. But then we also note that Martin Logan is now pumping out cheap crap from Canada instead of electostats from Kansas.

As you say, upconverting has solved many of the filtering problems of the 80s and 90s, but up and down converting include an implicit filter function. There's no free lunch. The upconverted signal does not sound identical to the base signal. This fact is central to DSP, both audio and visual - it's also understood at Pixar.

Your statement that we can make more nearly optimal filters today is incorrect. We're still using the math from the 30s and 40s: Butterworth, Bessel, Chebyshev, Eliptic. That math is optimal. It was optimal then, it's optimal now. But optimal is an engineering term. A perfect filter, as I presume you know, requires violating causality - you have to know the entire signal, past and future. If such a filter function existed, it would be proprietary property of Goldman Sachs or Warren Buffet and they would use it to all become billionaires. It would certainly not be available to squids like us.
Thank you. As an engineer and scientist, I hope you can understand my point of view here.

From the above, I got:

1. The conclusion that 18 bits was "better" than 16 bits was the result of uncontrolled sighted testing.
2. The conclusion was stated anecdotally without reference to the average results of the total test group.
3. "slightly better" has not been defined. Care to elaborate?
4. No criteria mentioned re: recording level re: 0dBFS, specific content, playback SPL reference, system gain, input system gain and acoustic noise floor, etc.

Because of the above I find it a bit of a stretch to put an awful lot of stock in the claim of 18 bit superiority as being reliably discernible. More recent testing has not revealed consistent differentiation between 16 and 24 bits in controlled double-blind testing.

And just a couple of comments:
1. CD sampling frequency is 44.1, not 44.056. The latter was at one time a possibility for the CD, but ultimately was rejected. It was chosen for the EIAJ consumer PCM digital recording system (Sony PCM-F1 and similar) that used video transports designed for NTSC color at 29.97 fps. The format was defined as 14 bits, but in Sony's products they dropped a bit of error code and added two more data bits per sample. The Pro gear of the early PCM/CD era (Sony PCM-1600 family used for CD mastering) ran at 44.1, used pro U-Matic decks set for "monochrome" at 30fps.

2. The CD maximum capacity re: Beethovens 9th, may have been a goal, but though the disc had sufficient capacity, the practical maximum was 72 minutes play time of a single U-Matic tape. Thus, the reference performance of that work couldn't be put on the original CD until U-Matic tape left the chain. The original reference performance, that of a 1951 mono recording by Wilhelm Furtwängler, noted to be the slowest performance of the piece. That piece would not be released on a single CD until 1997. The somewhat more famous Herbert von Karajan recording of the 9th symphony was played faster and fit on one disc. Von Karajan also participated in the early CD promotion.

(a good reference for the points 1 and 2 above is the paper Shannon, Beethoven, and the Compact Disc by Dr. Kees A. Schouhamer Immink of Philips)

3. The higher performance filters I mention relate to the common use today of digital over-sampling filters to improve performance over the initially all analog anti-aliasing filters of the early days. Yes, the math still has to work, but over-sampling changes a few things for the better, such as a relaxed requirement for the final analog filters, and the application of high-order FIR digital filters. I'm sure there's no need to explain this, but the result is a more nearly optimal filter as compared to high-order analog filters of several decades ago, both in the quality of the composite result and in the in-band phase performance. I doubt there's a single audio device in current production that still uses analog-only filtering today.

4. The "stereo is all but dead" comment seems a bit out of line with the facts. Yes, a lot of home systems have been sold that are capable of driving more that two speakers, but the very largest share of all recorded and released music today is still two-channel stereo regardless of the final container, a point not at all arguable. Two-channel stereo played on a multi-channel system most often defaults to two speaker channels only, with processing available that could extract more channels at the option of the user. Most users don't know the option exists. The brief flirtation the industry had with 5.1 music has become almost obscure. Car stereo is still two channel stereo, as is the massive headphone audience, arguably the largest segment of total music listeners.

5. I'm unaware of any CD players that used 12 bit DACs. 14 bit, yes, a few, but very few, like the Philips/Magnevox CDP-100. But that's perhaps just a result of my limited scope. The original CDP-101 that Sony brought in to us for the first CD broadcast in the US was a 16 bit. I think Philips tried to hang on to the 14 bit concept because they already had a 14 bit DAC chip ready to go.

Last edited by jaddie; 15th February 2020 at 07:58 AM.
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Old 15th February 2020, 08:21 AM   #98
scottjoplin is offline scottjoplin  Wales
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It appears you weren't satisfied with his test conditions after all.
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Old 15th February 2020, 08:26 AM   #99
abraxalito is offline abraxalito  United Kingdom
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The Philips players that used 14bit DACs (TDA1540) also used modest oversampling (SAA7030) to get better than 14bit performance (noise floor). In a similar way to DAC chips today using large oversampling ratios and noise shaping to give a 6bit DAC a 22bit noise floor. I've also never come across a 12bit DAC in a CD player.
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Old 15th February 2020, 09:10 AM   #100
jaddie is offline jaddie
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It appears you weren't satisfied with his test conditions after all.
I don't think we have all of the test conditions.

It's very hard to accept that any sort of research done at that level in academia would not have been conducted with the proper controls.
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