Hello from Texas.

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Re: Hello from Texas.

Postby RB Blackstone » Thu Jul 20, 2017 10:35 am

Good point on phase.

The first time one I heard 24/96 was the the first time the cymbals sounded right. Back then, there were analog filters ahead of the ad converter. A cutoff freq of 48k meant nasty phase and group delay down to 1k. Nowadays oversampling means your 48k converter is really 384k and the filtering is done digitally. A nice Bessel filter can be in the analog domain before that. Big difference.

I haven't done a serious listening comparison in awhile. Perhaps it's time. I do all work at 96/24 because it sounded better at that time and because it's in the Grammy Engineering recommendations.

https://www.grammy.com/recording-academ ... guidelines

I have heard great work at 48kHz and you get lots more DSP!
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Re: Hello from Texas.

Postby Doug Coulter » Thu Jul 20, 2017 8:33 pm

Yeah - if the frequency is low enough - say a kick drum fundamental, you can SEE it in the woofer cones, and I for one can tell pressure from suction on something like a snare drum hit (if it's loud, it slaps your chest, or doesn't, in the grossest manifestation).

I'd bet that the 96/24 reccie is just because that's probably now the cheapest & easiest way to get the eventual 44.1/16 right. Bits are cheap now on disk and in ram...and specsmanship means they just won't make the converters good enough at the lower sample rate and bitness. Further, if the engineer being pushed on by marketing is thinking he's going to do 24 bits of good...he might get 16 or even 18 in the analog part...

I bet you could make great money on the bullsht circuit writing articles about what those things actual measurements were. Except whoever printed them would instantly lose all the advertising dollars. I quit the audiophool biz over not being able to tell the truth.

It was a lot trickier in the old days when your 486 or Pentium I might not be quick enough to be useful for audio editing of any complexity (and forget a real time FFT display). Our first board had to have a big DSP on it to offload the PC enough to do fun stuff, and yeah, at that point it paid to just have the better converters and front end stuff, as those backend bits weren't cheap at all...back in the day.

When we were able to have a real time spectral view and filter previews while you adjusted things for the first time - David Johnston of CoolEdit fame quoted "Quantity has a quality all it's own".

No one had been able to handle that level of computation in real time before and it really made a difference, there and in real time previews of any effects. Back then, it wasn't normal to be able to do those kinds of things. Now it's not a real program if it can't.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Hello from Texas.

Postby RB Blackstone » Mon Jul 24, 2017 5:04 am

Wow, you were there when it had to be assembly language to run fast enough.

I remember when HTML wa introduced. I thought how wasteful to use all that bandwidth for a picture. Lol

I just saw the mention of the lm194/lm394 in the analog forum. One of the guys that really helped me when I was a kid was Deane Jensen. He designed the discrete 990 OpAmp that is still revered in pro audio. I read everything I could on the design of that 990. Central to the design is the lm394. They were discontinued in 2010. I don't know if anything is made that fills that void.

Here is a link to the 990 lit. From the Audio Engineering Society paper

http://www.technicalaudio.com/pdf/Jense ... t_1980.pdf
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Re: Hello from Texas.

Postby Doug Coulter » Mon Jul 24, 2017 10:24 am

I was there when assembly on a PC processor had no hope of being fast enough!
We used a nifty lashup with a TMS 320-c31 DSP, which was mapped such that when it went to boot, it tried to read the ISA bus registers and got hit with a wait signal till the PC wrote things to those (32 bit) latches (which were later used for bidirectional comm with the PC). Since the C31 always read its boot rom sequentially, we could just map the entire address space it defaulted to to the PC interface. Ditto, if the PC tried to read or write those same latches (one set per direction) and they were empty or full respectively, the PC got a wait line pulled on it. We hit something greater than 3 megabytes/second on the isa bus using the single address 32 IO instruction with the repeat prefix.

Unlike the Intel stuff at the time, the C31 could do around 5 things per clock...otherwise it looked kinda like a motorola 68000 or going back further, a PDP-11 (separate address and data registers like the 68k, but data registers were floating point natively and separate ALUs for addresses and data.
Like the PDP, though, all the registers were just "there" so you could easily do computed jumps by adding to the PC and mess with the stack pointer and so forth.). Ours was fitted with all no wait state static ram, and originally some Burr-Brown successive-approximation A/D and D/A converters.
A PIC uP was used to make sure we didn't hold the PC hung for too long in the case of error, and some GALs were used for the control logic and address mapping.

Later, when they got better we were able to go to some sigma-delta ones (we got 18 bit ones and just used 16), but they were never as good - just ~ $200 cheaper. Bill gave me an old Pentium II mobo for display, but when we did this it was 486 and P I all the way...
100_3199.JPG
The old C-Lab Musicad board

I almost broke even on this one...others took the ideas and ran with them, which was fine - the market was broke musicians with some of daddy's money, duh, bad business move on my part. But it turned out great - the subsequent consulting and product design business used this as a demo of my skills and virtually no salesmanship was needed thereafter to get all the good work we wanted...winding up at ~ a million bucks a year per guy before we shut it down from burnout. We thought we were pretty hot stuff in the day, and we had the paychecks that meant we weren't alone thinking that. Of course, in hindsight a lot looks pretty silly.
http://www.coultersmithing.com/OldStuff/CLAB/index.html



BTW, I have some LM 394's in the junk box and have used them, primarily for moving coil preamps where they really shine for low noise voltage at relatively high collector current to match that low impedance input, the basic design taken from the National Apps handbook of '78 (which in turn was stolen from a marantz design used in their tone controls, pre-sony). Our "fine wine" preamp is an extension of those principles. But there we didn't mind asymmetric time response and wanted lowest noise at a very high input impedance, so we used different parts and other speeds and feeds.

Diff pairs have ~ 3dB more noise than single ended (in theory...). That DC coupled NPN-PNP we used in fine wine which was based on "the ultimate preamp" which was around the same time as the National (or Marantz) design has some good properties too - but tends to have 2nd harmonic distortion at the limits as the transistors both turn on a lot quicker than off. In our case, with phototube input that is fast attack and slow decay, it works out as a matched filter for the signal anyway.

Somewhere, from that same apps handbook, I've got the original tutorial on how to design opamps or in fact any feedback amp with good bandwidth and slew rate - all proceeds from that - physics is physics and the rules haven't changed. It was a real eye-opener that you needed to reduce the transconductance of the input pair to get any slew rate and still be able to close the loop. This is why the fet amps stormed the world at first, they were the first really quick enough to do audio well. Then lm837 (?) and pals, bipolar again. My modification of the Dan Meyer amp (tiger .01) to use fet outputs also reduced the transconductance of the input stages with larger emitter resistors, and burned more current for speed at the cost of some more voltage noise, still not bad, and I still use it in my reference stereo today. (I should document that thing, it's really good, DC->4MHz, distortion so low it was very hard to measure, around .0027% IMD at 30 and 31 KHz 1::1 and full power - any other case I couldn't measure at all with custom built help for the distortion analyzer). I don't appear to have the scans of that tutorial online at the moment, when I get a round tuit I'll scan them and put them up. It's the really good stuff...(finding things when you have so many can be the hardest part, they're probably up there somewhere...)
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Hello from Texas.

Postby Doug Coulter » Mon Jul 24, 2017 10:35 am

Holy crap, the good stuff lives on! Ti now has this online! Worth your time.
http://www.ti.com/lit/an/snoa737/snoa737.pdf

And check figure 4 in this:
http://pe2bz.philpem.me.uk/Parts-Active ... orSets.pdf
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Hello from Texas.

Postby RB Blackstone » Mon Jul 24, 2017 4:59 pm

Wow. You amaze me. I know the DSP book. I hadn't connected the book to the dude with a reactor. Lol

The unordered list. Very cool.
"Specialization is for insects." - Robert Heinlein
That stuck with me the first time I read it in my teens. Sure, I could get someone to fix the window. Sure, I'll break the first one I try. After broken window version 1.0, I'll have working window 2.0 and will have gained some skill.

I am told the LM394 replacement was the MAT02 until it was discontinued. The replacement is now the MAT12. FYI.

-RB
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Re: Hello from Texas.

Postby Doug Coulter » Mon Jul 24, 2017 7:47 pm

The book kind of stank...it was my first try at that, and they took out all the cool stuff - those little girls with apple grammar checker etc that couldn't understand a pun, and so on. At least I recovered from the carpal tunnel.

My only defence is that at the time, there was NOTHING else but IEEE stuff that no one else could understand if they also had time to know anything about the real world too.

The editor for that book was a "true believer" in both UFO's and Bill Clinton. I rest my case; the original was a lot better.
But we did give away the code for free, though it needs serious work now to run on windows, since they finally ditched the crazy 16 bit mm stuff.
I'd guess dev studio wouldn't even build it now, but of course, if you've got any of it, feel free to use the code bits - at least that part is good.

The book sold in excess of 35k copies, but...according to the various publishers it's been sold between, I've sold negative copies (how?) and have gotten zero royalties, so DON'T BUY THAT BOOK. If I can find it and anyone wants it, I've got a copy of the CD it was on somewhere.

How do I know how many sold? I don't, actually. I just know how many emails I got from unique addresses because while they did their best to sanitize the text, my email address was in the code...

Frank Zappa was right about "hollywood accounting". Were I to do that again, I'd self-publish. Oh, wait, that's what I'm doing now, and the pay is the same but it's more fun.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Hello from Texas.

Postby Fredd Bergman » Sat Sep 23, 2017 4:57 pm

Hey RB. I just signed up for this outfit, too. Mostly to read and learn.

I think I met you during the 80s. I was a jock on KSYM and several gentlemen's clubs. Ran around with guys involved in SA's music scene. Maybe I'll run into you again.

DD
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Re: Hello from Texas.

Postby RB Blackstone » Sat Sep 23, 2017 6:52 pm

Hello!

What a surprise. Yep, that's me.

Playing with Funkasaurus Tex and still doing studio production.

According to Heinlein, only insects are specialists.

The incredible brain trust here handles concepts that are very advanced.
Many of those concepts reflect new ideas back to my world.
Fascinating.

Take care and thanks for saying hi,
RB
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