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Author Topic: S/N in big consoles  (Read 13882 times)

bruno putzeys

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Re: S/N in big consoles
« Reply #15 on: January 19, 2011, 12:46:59 pm »

Ultimately you have to leave it. What I'm talking about is leaving it to mix in the analogue domain and then turn it back into digital.
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Warp Drive. Tractor Beam. Room Correction. Whatever.

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John Roberts {JR}

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Re: S/N in big consoles
« Reply #16 on: January 19, 2011, 01:02:59 pm »

A philosophy but not scientific thesis. One could argue analog is just a bunch of discrete quanta massed in large enough numbers to appear continuous.

At some point digital becomes another piece of wire (which isn't perfect either but like so what?).  Perhaps more correctly digital will be like wire with some small flat colorless delay which does need to be managed for OTB mixing of mixed analog and digital stems, especially if coherent signals are split across multiple stems, but again not a new concept in recording, and managing delay inside a digital final mix is not a huge issue with adequate clock resolution.

We are several decades into digital being a merchantable medium. The SOTA is quite good and getting more affordable. Perfection is a concept not a destination. It can't be attained in either medium.

There are still many details to work out as digital is less mature than analog, but past the wet behind the ears stage IMO, and I'm an old analog dog...pedaling as fast as I can to keep up.  

JR

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Bob Schwenkler

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Re: S/N in big consoles
« Reply #17 on: January 23, 2011, 02:51:18 pm »

John Roberts  {JR} wrote on Wed, 19 January 2011 08:15

Back in 1980 I wrote an article on console design for RE/P where I described a way to bus numerous channels together without the N+1 noise gain of a virtual earth summing amp (replace the resistors with current sources).

Is there available or do you have a copy of this article?

dcollins

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Re: S/N in big consoles
« Reply #18 on: January 23, 2011, 10:22:59 pm »

John Roberts {JR}

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Re: S/N in big consoles
« Reply #19 on: January 24, 2011, 01:01:07 am »

Bob Schwenkler wrote on Sun, 23 January 2011 13:51

John Roberts  {JR} wrote on Wed, 19 January 2011 08:15

Back in 1980 I wrote an article on console design for RE/P where I described a way to bus numerous channels together without the N+1 noise gain of a virtual earth summing amp (replace the resistors with current sources).

Is there available or do you have a copy of this article?


http://www.circularscience.com/des_art.pdf

The references to SOTA are a little dated since I wrote this over 30 years ago, but it holds up OK (I hope).. Only thing I am embarrassed about is I spelled bus wrong back then...   Surprised   But some still spell it wrong today.  Laughing

JR
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zmix

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Re: S/N in big consoles
« Reply #20 on: January 24, 2011, 10:51:20 am »

dcollins wrote on Sun, 23 January 2011 22:22

Has anyone read this!?

http://collinsaudio.com/Muth_Summing/


DC



Hmmm.... his assertions from 2002 seem more dated than JR's from 1980 (and John stated that he can spell Bus correctly now so he goes to the head of the class!!)

I'd like to see the Geoff Tanner Article Chris referenced...

You out there Geoff?

John Roberts {JR}

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Re: S/N in big consoles
« Reply #21 on: January 24, 2011, 12:17:30 pm »

dcollins wrote on Sun, 23 January 2011 21:22

Has anyone read this!?

http://collinsaudio.com/Muth_Summing/


DC


I have never seen this before, and it starts out with one strike against it, since it spells bus wrong, but I was guilty of that for a time, before I figured out what the right word is in the context of combining signals, and what the wrong word really means (look it up). Laughing

OK, from a quick glance at the article I see several claims that jump out at me.. Since the document is copyrighted I will paraphrase.

#1 The more inputs to a system the more losses.   (pg 3)

That may be an awkward way of relating the increasing noise gain of a "lossless" (not my nomenclature) virtual earth summing system, but as I published a few decades ago, there are other ways to skin that cat without the linear increase in noise gain.

#2  twice as many inputs = twice the bus noise.. (pg 5-6)

The math is a little sloppy as incoherent noise sources do not add linearly, but my larger criticism of the comment is that source noise will still dominate console noise, even for large consoles (I have designed at least one console with 100+ feeds to L/R bus).

#3 digital combining cost 1 bit of (?) for every doubling of stems. (pg 7)

I'm basically an analog dog, but I do enough digital crunching to know that is nonsense.  Simply adding together multiple digital signals results in the exact same digital word resolution. Headroom or bus overload is exactly the same as analog, but digital can use a carry bit to buy another 6dB of dynamic range transiently.

If you combine with a multiply (digital fader/pan gain adjustments are preformed by a multiply) You actually gain resolution in an output digital product with even more bits! In fact the result will have the bit resolution of the input word, added to the bit resolution of the multiply word, or more bits than we can typically use or care about.

#4   Dither?

This seems to be a red herring, Dither is pretty well understood by now (I think).

#5  A mix of 64 sources needs to run -36dB   (pg 8 )

Again. sloppy or misinformed math. Perhaps for 64 identical sine waves but 64 incoherent sources only increase +18 dB, and we don't build mixes with 64 inputs all at full gain, all the time.


===================

Sorry, this paper reads like a marketing tout masquerading as technical information so caveat lector.  I really wish a fraction of those claims were true, because if there was a real benefit to mixing in the analog domain, I would have the technological edge to promote (my current source summing).

I have been searching for some actual critical flaw in digital combining for years and I haven't found it yet.

I would take this paper with a grain of salt (the size of a deer lick).   Rolling Eyes  As I have said several times, there are real performance consideration when combining a large number of analog stems, but noise is not the dominant one (distortion and phase shift are real consideration on the scale of that paper's comparison). Digital on paper at least, seems to have the edge.

JR

PS: For the record I have nothing on sale here. I have been out of the console/mixer business for more than a decade, and I see little reason to promote a technology that has been eclipsed by digital. I still have friends making and selling analog consoles but they don't resort to such merchandising.
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bruno putzeys

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Re: S/N in big consoles
« Reply #22 on: January 24, 2011, 01:43:18 pm »

You just saved me quite a bit of time replying there...
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ssltech

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Re: S/N in big consoles
« Reply #23 on: January 24, 2011, 02:38:58 pm »

Back when that paper was current, I voiced similar comments, and Chris Muth registered and posted some rebuttals... Several people whom I respect all dig Chris's work, and I've used some of his product before and it's certainly been very well made. -I wouldn't wish for a second to impugn his abilities or his product.

None the less, I'm glad that I'm not the only one with these impressions regarding the paper.

-Keith
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MDM (maxdimario) wrote on Fri, 16 November 2007 21:36

I have the feeling that I have more experience in my little finger than you do in your whole body about audio electronics..

zmix

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Re: S/N in big consoles
« Reply #24 on: January 24, 2011, 02:59:58 pm »

Yes, thanks John...!  (I edited my initial response to the "buss" paper 3 times to maximize politeness...  Rolling Eyes )

Geoff Emerick de Fake

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Re: S/N in big consoles
« Reply #25 on: January 25, 2011, 07:30:45 am »

Hey, what's wrong with a fishing boat?  Laughing
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dcollins

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Re: S/N in big consoles
« Reply #26 on: January 25, 2011, 06:44:35 pm »

ssltech wrote on Mon, 24 January 2011 11:38

Back when that paper was current, I voiced similar comments, and Chris Muth registered and posted some rebuttals... Several people whom I respect all dig Chris's work, and I've used some of his product before and it's certainly been very well made. -I wouldn't wish for a second to impugn his abilities or his product.



That doesn't mean the gear won't sound great, but I was just surprised that both the analog and digital conclusions were off the mark.

Was the paper ever revised?


DC

John Roberts {JR}

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Re: S/N in big consoles
« Reply #27 on: January 26, 2011, 02:56:11 pm »

dcollins wrote on Tue, 25 January 2011 17:44

ssltech wrote on Mon, 24 January 2011 11:38

Back when that paper was current, I voiced similar comments, and Chris Muth registered and posted some rebuttals... Several people whom I respect all dig Chris's work, and I've used some of his product before and it's certainly been very well made. -I wouldn't wish for a second to impugn his abilities or his product.



That doesn't mean the gear won't sound great, but I was just surprised that both the analog and digital conclusions were off the mark.

Was the paper ever revised?


DC




I don't mean to cast aspersion on the product or person.

My comments apply to the claims made in the paper in your link.

I will leave it to others to speculate about any connection between that paper and product. I have met, and worked with my share of marketing types who were clueless about the minutiae of design philosophy.

I recall following one co-worker around at an AES show to attempt damage control on the spot. He had memorized a bunch of buzz words from listening to my spiel, but couldn't string them together into a intelligible sentence.   Laughing   Bless his heart he was a selling machine, but an embarrassment to me when I was within earshot.  


caveat lector.  

JR

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JGreenslade

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Re: S/N in big consoles
« Reply #28 on: January 27, 2011, 06:04:24 pm »

Geoff_T wrote on Wed, 12 January 2011 18:47

Hi

Vintage Neve consoles had signal to noise measured in three stages.

1. The output noise with the 4T fader at minimum... usually up around high 90's

2. The output fader up and a single channel assigned to the 4T bus

3. A channel at 80dB gain assigned to the same path with 20 to 20KHz filter on all these measurements and the input terminated 200 ohms. That last test gave figures better than -45dB = EIN better than 125.

But note, they did not assign all the channels to a bus... just one channel.

All these tests are clearly listed at the rear of the technical handbooks along with a polaroid photo of the square wave response.

Plus all vintage Neve tests were referenced to 0dBu, not +4dBu and the noise was not subtracted from the maximum output like digital measurements these days and power amps.

Hence their wonderful figures!



This reminds me of a chat I had a while back with a certain pipe-smoker who looks after a gaggle of vintage Neves here in the UK. A client had remarked that, whilst their facility could live with the console's noise floor, they were interested in bringing it below that of the new-fangled hard disk recording devices. Said engineer decided to try an experiment, by equipping a selection of bus amp cards with uber-low noise Japanese epitaxial types (the type developed in the eighties for low noise MC cartridge preamps), putting these in place of the original cards that contained BC184s and seeing what difference this made to the broadband noise trace on the FFT...

...suffice to say, there was no difference at all. The transistors themselves are by far one of the least dominant noise sources - as I'm sure the Neve stalwarts here will be fully aware. I just thought it would make an interesting interjection to relay the tale. I guess he wished in his heart that he could walk away from the studio feeling smug that he'd taken 12dB off the console's floor... No cigar that day!

Justin
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John Roberts {JR}

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Re: S/N in big consoles
« Reply #29 on: January 27, 2011, 11:46:04 pm »

JGreenslade wrote on Thu, 27 January 2011 17:04

Geoff_T wrote on Wed, 12 January 2011 18:47

Hi

Vintage Neve consoles had signal to noise measured in three stages.

1. The output noise with the 4T fader at minimum... usually up around high 90's

2. The output fader up and a single channel assigned to the 4T bus

3. A channel at 80dB gain assigned to the same path with 20 to 20KHz filter on all these measurements and the input terminated 200 ohms. That last test gave figures better than -45dB = EIN better than 125.

But note, they did not assign all the channels to a bus... just one channel.

All these tests are clearly listed at the rear of the technical handbooks along with a polaroid photo of the square wave response.

Plus all vintage Neve tests were referenced to 0dBu, not +4dBu and the noise was not subtracted from the maximum output like digital measurements these days and power amps.

Hence their wonderful figures!



This reminds me of a chat I had a while back with a certain pipe-smoker who looks after a gaggle of vintage Neves here in the UK. A client had remarked that, whilst their facility could live with the console's noise floor, they were interested in bringing it below that of the new-fangled hard disk recording devices. Said engineer decided to try an experiment, by equipping a selection of bus amp cards with uber-low noise Japanese epitaxial types (the type developed in the eighties for low noise MC cartridge preamps), putting these in place of the original cards that contained BC184s and seeing what difference this made to the broadband noise trace on the FFT...

...suffice to say, there was no difference at all. The transistors themselves are by far one of the least dominant noise sources - as I'm sure the Neve stalwarts here will be fully aware. I just thought it would make an interesting interjection to relay the tale. I guess he wished in his heart that he could walk away from the studio feeling smug that he'd taken 12dB off the console's floor... No cigar that day!

Justin


If those are the devices I am thinking of they date back to before the '80s. The 2SB737, and 2SD786, nice very low noise, down around .35 and  .4 nV/rt Hz. I actually used them in MC preamps, and mic preamps back in the day. They are obsolete now.

JR:
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