John Curl's Blowtorch preamplifier part II - Page 1708 - diyAudio
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Old 29th October 2011, 12:21 AM   #17071
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Well, this one is actually not PCM but it claims an analog SNR of -116dB.
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Old 29th October 2011, 12:22 AM   #17072
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http://www.grimmaudio.com/product_info/Manual%20AD1.pdf
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Old 29th October 2011, 12:28 AM   #17073
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-116dB is still a substantial distance above 24bit quantization noise. It's equivalent to around 20bits.
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Old 29th October 2011, 12:30 AM   #17074
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Quote:
Originally Posted by simon7000 View Post
Now if you allow the premise that some humans (I know a presumption on my part) can perceive distortions of -140 db to -160 db re the peak sound pressure level, then many of these issues would actually have a basis!
I don't. There is no evidence in any context for this exaggerated claim. At some point you have to stop sending random resistors to folks and asking for their uncontrolled anecdotal comments and presenting it as evidence.
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Old 29th October 2011, 02:17 AM   #17075
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> At some point you have to stop sending random resistors to folks
> and asking for their uncontrolled anecdotal comments and presenting
> it as evidence.

And how do you define that 'point' ..........
I'll take some of your samples .....
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Old 29th October 2011, 02:28 AM   #17076
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Quote:
Originally Posted by hitsware View Post
> At some point you have to stop sending random resistors to folks
> and asking for their uncontrolled anecdotal comments and presenting
> it as evidence.

And how do you define that 'point' ..........
I'll take some of your samples .....
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You make up some test where some resistors measure -140dB vs -150dB distortion and then you send those resitors to a third party and ask them to use them in some circuit and they line them up in your empirical model of what matters. And then you claim this means that stuff at the -150dB level matters.
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Old 29th October 2011, 03:02 AM   #17077
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Over the decades, we hi end designers have discussed differences in resistors. Audio designers used to use carbon resistors, sometimes 'lousy' carbon resistors as standard. Allen Bradley in the USA seemed to make a pretty good carbon resistor, and Ampex used them for everything except precision attenuators. Back in those days, a 1% precision resistor might cost the equivalent of a cafeteria lunch.
Still, exceptions were found in resistors that added excess noise or distortion. As our measurements got better, we noticed this more. Richard Heyser pointed this out to me, over 40 years ago. In the 1980's 'HFN' came up with an article that measured distortion in both caps and resistors, AND they even tried to evaluate them by listening. They did a very good article.
In any case, all my best designs include specifying certain resistor brands and size. It is part of the design process for me, and I will stick with it. By some coincidence, one of my favorite resistor brands, the German made 'Resista' the standard component in my Vendetta Research phono stage and the Blowtorch, MEASURES really well, compared to some other Resistors, and they only cost me $.05 in limited quantity of 100 or so. Today I rely on Ed Simon to guide me on what is still available and how well it works.
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Old 29th October 2011, 07:05 AM   #17078
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Quote:
Originally Posted by abraxalito View Post
-116dB is still a substantial distance above 24bit quantization noise. It's equivalent to around 20bits.
The best high-end mastering converters have 127dB SNR that is equivalent to 21 real bits of audio. The remaining 3 bits are noise. This is the maximum that is possible to obtain considering the difference between the Johnson noise and the maximum levels used in balanced proaudio (0Vu = +4dBU vith 24-26db headroom) which is way more than the -10dBV used in unbalanced hifi. So there is no real chance to improve this 127dB, except if the whole level standard would be changed to a much higher one (no chance) or to imerse the whole converter into liquid nitrogen to reduce Johnson noise.

Anyway even if it would be possible it wouldn't matter because the SNR situation is already compromised long before any AD or DA conversion at the microphone and mic preamp.

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Old 29th October 2011, 08:20 AM   #17079
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Permanent mismatch here between narrow band FFT resolution and SNR calculated over whole 20kHz width of frequency band - as in any amateur discussion.
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Old 29th October 2011, 09:48 AM   #17080
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Permanent mismatch here between narrow band FFT resolution and SNR calculated over whole 20kHz width of frequency band - as in any amateur discussion.
Well, that and the failure to distinguish resolution from signal-to-noise.
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