Hello from Texas.

Post here once you join, and tell us about yourself so we have a clue who we are talking to.
Keep threads short here -- once you have something to say, there's a topic here somplace where it will fit -- and if not, let me know and I will make subforums as necessary. We want all of hard science and tech up here, and if something doesn't fit -- that's my fault and I will fix that for you. See the rules and tips in the parent forum, please.
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This sub forum is for new menbers to announce themselves. Try not to create long threads here -- this is just for you to tell us who you are, and for us to say welcome. There are other forums to actually discuss real tech-science things here, and ask questions on. The idea hopefully is to have enough forums and subforums that nothing sci-tech related will be off-topic, there will be a place for it. If I missed something -- let me know, and I'll fix that.

Hello from Texas.

Postby RB Blackstone » Sat Jun 24, 2017 2:01 pm

Hello,

RB here. I am enjoying reading through the posts on the board. Nice to see such a high signal to noise ratio. That only come with a lot of moderator work. Thank you

My interests are wide and whacky. This is a general list.

Recording Engineer and producer. (Since analog tape and vinyl)
Musician, arranger and keyboard guy.
Math, electronics and physics geek.
Student for life.

Nice to meet all of you and I look forward to learning a lot!

Thx,
RB
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Re: Hello from Texas.

Postby Donovan Ready » Sat Jun 24, 2017 2:03 pm

Hello back from Texas.

We are all students for life, or should be. Welcome.
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Re: Hello from Texas.

Postby Doug Coulter » Sat Jun 24, 2017 2:18 pm

Welcome from VA, too.
We got lucky on the SNR, but it's been some work - anybody here with a green name deserves thanks and props, they've all helped.
Main thing is how we're set up here. Some crusty old guy (me) is a jerk and won't let in just anyone - work up front, but really after that, we don't have all that much to do once any mistakes by that guy are taken care of.

We really kinda have a multi part thing going on here. We have announce yourself (here) - so we know who we're talking to and will try not to go over or under your head and that's your thread to do with as you please (Well, keep it legal). We also have the water cooler where almost anything goes - if anyone, even the old guys, have questions, that's usually where they belong (I cheat some, but it's my bat and ball). We haven't made that accessible to the new guys yet, but we may change that. For now, playpen is for questions.

The big exception is if your're documenting a big project and run into a snag on it - now that we have context from your previous posting, we might know the answer and give it on your project thread. Those are the rest of the board, where we are attempting to "Write the book" on how those who do things for real, actually get them done, how to hold your mouth and stuff like that. We guard that kind of closely, as that's where the SNR is the best - by design. We're not letting the new guys do that directly, yet. That's what playpen is for at the moment - have fun there.

We added playpen for the new people, It's like water cooler, in that it self-empties after no interest is shown in something for 20 days or so, but it's your chance to show your stuff - if we like it, it gets promoted to the right part of the board for that topic, and likely we promote you too so next time you just post in the right place and everyone saves effort. Right now, playpen and announce yourself are the only places new guys can post...but once we figure out you're ok, and it looks like for the most part I got that right from the get go - ~ 50 guys let in out of ~ 1000 trying - you're really in. Maybe you even turn green yourself if you do good things.

BTW, I did a lot of the original DSP nonlinear editing audio hardware/software, you'd know the names if I dropped them, but I started with tape and vinyl too. I had Bing Crosby's Ampex 1/2" 4 track "tape stretcher" and built a DBX kind of thing for it and made it punch able for overdubs.
Then 8 track 1/2" then...digital. I got happy with that and am done in that biz now, but I still play some just to keep myself happy. I still have some killer audio stuff, but nothing beats just doing it on the instrument -100% reality, eh?
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 » Thu Jul 06, 2017 1:57 am

Very cool!!!

The writing here reminds me of the net pre HTML. Everyone could spell and advertising was forbidden.

I imagine I would recognize the non linear systems you worked on. I was one of the geeks that made the transition from analog to digital and remember seeing the first demos at the Audio Enguieering Society conventions.

I still have a pack of the 8" floppies that SSL used to store mix automation.

There's a D'Angelico guitar at a studio where I'm playing B3 on Saturday that toured with Bing Crosby for years. It exhibits a phenomenon that I've never heard before. It's the volume at 3 feet as it is at 12 feet.

Never did get a chance to work on the Ampex machines. That's mainly happenstance. I worked on MCI, Studer and Otari Used plenty of Ampex tape though. I just baked a few last week for a transfer.

Well, gonna go wander the board and read for a bit or several bits.

RB
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Re: Hello from Texas.

Postby RB Blackstone » Thu Jul 06, 2017 4:19 am

Well, I enjoyed wandering.

Very impressed with preamp design.

"FSCK you very much" is hilarious. I may borrow it, but I'll give you credit.

G'nite.
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Re: Hello from Texas.

Postby Doug Coulter » Thu Jul 06, 2017 2:18 pm

That design is an evolution of the old "ultimate preamp" from Popular Electronics way back. Here it's been optimized to act as a pulse-shape filter in the sense that is has very fast attack and slow decay (would create 2nd harmonic distortion in audio near the slew limit) and a frequency response that matches the most common detectors (matched Wiener filter for the expected signal). That can (mostly) be changed via changing some R's and bias current points. Unlike audio, that one doesn't float in the middle of the output range, but at the top, for negative going pulses. So, just optimized for that one main use. A slow but quiet transistor is used in the front end for noise reasons and to deliberately low pass the signal. It's a case of "beware the parts that aren't there in your analysis" because if you pick the right ones, you don't need more parts.
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 » Tue Jul 18, 2017 3:29 am

Wow. "Slew Limits"

There was a great study of slew induced distortion by Reginald Williamson some time back.

I suspect that is the mechanism in play when I track through a pro ad converter at--18 to -12dBfs and people think it sounds analog. The analog section doesn't have to wiggle so hard.

RB
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Re: Hello from Texas.

Postby Doug Coulter » Tue Jul 18, 2017 8:09 am

FWIW, the problem still exists. Sigma-Delta converters used in digital audio often slew limit if high power at high frequencies is applied or generated.
We even put sweep generators in our musicad software to show this (and CoolEdit IIRC) - it could get really gross.

Thus providing the audiophile discussion with yet more grist for the mill and endless argument about the wrong stuff - "proving" that super high sample rates and bit depth are required for the best sound.

When something that actually manages 16 real bits and 44.1 real kHz is actually better than almost anyone's ears and certainly better than the rest of the chain by a long shot. Thing is, 99.9xxxx% of converters rated like that start slew limiting hard at full input/output and under 10kHz...
From distortion to actual birdies and aliases...

Our first digital audio stuff used successive approximation converters that cost ~~ $80 each. Current stuff uses sigma-delta ones with variable goodness at $2...not that price is the determinant, but you do not get what you don't pay for most often.
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 » Tue Jul 18, 2017 7:03 pm

When digital became mainstream, (think Alesis Adat and Tascam d88 - circa 1992 ish) the converters were not that bad, but the analog I/O was PC soundcard cheap. Decades of knowledge were ignored. People would say "I have digital, but it doesn't sound as good". They were comparing a cheap mic through a Sound Blaster card operated at the wrong level by a home recordist to a Neumann U47 through an API console to an MCI 2" 16 track with discrete circuitry operated by a pro recording engineer. Lol.

They are just now getting the analog sections up to 1970 quality. I track at 24bit / 96k. That is some theoretical 144 dB of dynamic range. Plenty of bits in the capture bit depth. Air conditioning or fender twin noise makes it 10 bit in the real world. There is so much misinformation about levels. I wish recording gear would show operating levels and place 0 there instead of at full scale. The zero on a VU meter was roughly 18 dB below clipping. I operate at the American SMPTE level which is -20 dBfs = 0VU = + 4 dBu. This makes the old outboard gear and converters all happy and avoids slew rate distortion and other non harmonic distortion.

The only time the level is raised is in final mastering. That is a whole 'nother discussion.
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Re: Hello from Texas.

Postby Doug Coulter » Wed Jul 19, 2017 11:34 am

I won't disagree that the analog stuff was crap - too. We found that to get a real 16 bits worth of good it was super challenging - and we put our a/d and d/a converters in a separate pod outside the PC and away from the internal noise.

Still the sigma-delta (or delta-sigma) one bit -> filter -> lotsabits converters, while having neato dynamic linearity, also would slew limit at low
levels and high frequencies that even a TLO-84 would easily handle, and in doing so, would produce alias frequencies, not just harmonic distortion we all found the aharmonic tones a lot more objectionable. Many of them still have this issue, which is why people think you need 96khz/24bits (or more) - they run into this less, but it's not inherent in either the bit depth or the sample rate, it's that the converters are "better" -- clock internally faster and suchlike, so they don't run into this till higher levels and higher frequencies.

There is a very simple way to test this with a d/a - just generate a sine mathematically and play it back at various levels and listen to it. It's obvious when you make a 15khz tone and there's all these birdie tones down in the single khz and below range as a result. You can do the same thing going the other way with a decent signal generator and recording from the a/d. We in fact built this ability into MusiCad and CoolEdit back in the day.
There is no way an opamp makes this kind of spurious stuff.

Again, a true 16 bit - with its full dynamic range - is more than the ear can handle anyway - if everything else does its part. Yes, when I was young I could hear above 20khz a little (long gone). But most can't. With practice you can also hear phase of say, a bass drum, though in theory, you can't.
You yourself mentioned not using the full theoretical dynamic range. My fellow musician/studio guy JohnB who I worked with for decades says the same thing about current gear. It makes my point, actually. With very fast slewing sounds - say a cymbal hit with a hard tip drumstick - things just aren't right at high levels and low sample rates...but it's not the analog stuff (always, anyway, obviously anything can go wrong).

Again, a simple test as described above should show you what I'm talking about. My email sig is "Why guess when you can know? Measure!" for a reason.
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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