John Curl's Blowtorch preamplifier part II

[fas42]

Originally Posted by Telstar

There is life above 20khz
I posted a nice link a few pages ago.

Good point about the manipulated highres material issued for audio-phools.
But 2L recordings are not such, and the DXD masters are of amazing quality, ESP. If NOT downsampled.
.

Sorry to say, it is the 2L samples that have been doctored. I'll go the next step, and dissect 384, 192, and 92 versions of the same track, one of the examples from that website. Also, I'll take the 384 version, downsample to 92, then resample that back up to 384 and post difference files -- to prove nothing significant is lost or gained.

Why am I confident? Because I've already done this exercise on other files, some time ago, and got effectively null results on doing a difference ...

Frank

[fas42]

Originally Posted by kgrlee

Frank I think you were asking about detailed microphone distortion measurements over a large frequency range. I can say these are quite hard to do from experience circa 1980. The only published stuff I've seen is several Sennheiser AES papers where they show the THD advantage of their symmetrical RF mikes.

However, the 'conventional' evil examples in their paper are not really representative and it is trivial to have better performance. Their mikes are excellent but in fact suffer early overload for other reasons which might be more important to a recording engineer.

Thanks for that. I guess the material wouldn't be out there, on-line, though ...

So, everyone "knows" that certain mic's are excellent, even though one can't see figures anywhere, "proving" it. How do the engineers know? Because, they listen on headphones to the result, and of course headphones have a much, much lower level of distortion than mic's, because otherwise this wouldn't make much sense, would it ...?

Talk about a dog chasing its tail ...

Frank

[kgrlee]

Originally Posted by gpapag

http://www.drewdaniels.com/audible.pdf

Thanks for this George.

It's a pity they didn't list the zillion SACDs they used so we could exclude them from our tests.

Note the test was also about 16b vs "zillion or 1 bit" and not only about supersonics.

[SY]

Originally Posted by PMA

Show me measurements, SY, of that "nonsense".

Read any of my articles. I show my measurements. Additionally, Jack Walton has built my circuits and repeated the measurements, which are all posted on his website.

I have three preamps in the house at the moment, ranging from 0.002% 2nd to 0.03% second at full output. All single ended, all tube, all with no loop feedback, no SRPP or White. The measurements are all published. You can also look at Morgan Jones's designs- again with published measurements. Ditto Allen Wright's circuits. There are undoubtedly many more.

So, yes, the idea that well-engineered tube circuits have audible levels of distortion is nonsense unless you're claiming to be able to hear those levels of 2nd harmonic (which totally dominate the distortion spectrum- all other harmonics are 20 or more dB lower). I would find such a claim... difficult to believe, in the same category as, "I can dead-lift 1000 kg with one hand!"

[dimitri]

M. Killion, A Low-Noise Two-Wire Condenser Microphone Preamplifier, JAES April 1967

[Speedskater]

Originally Posted by kgrlee

***********************
PMA, do you know if the vintage Telarc stuff issued shows dynamic range above 20kHz? From what I know about their mikes, it is possible.

*********************

In a typical Telarc recording, it could be 10 meters or much more from the microphones to any musical instruments that have any content above 20 kHz.

[scott wurcer]

Originally Posted by dimitri

M. Killion, A Low-Noise Two-Wire Condenser Microphone Preamplifier, JAES April 1967

Gee Dimitri are you saying that someone realized the same thing in 1967 surprise, surprise, surprise? I like the wording (BTW there is a bit of history about Johnson and Nyquist and near simultaneous discovery). I still find Nyquist's example and reasoning a wonderful model of clear thinking.

[SY]

According to the reference, it was more like 1940.

[fas42]

Originally Posted by fas42

I'll go the next step, and dissect 384, 192, and 92 versions of the same track, one of the examples from that website

The 2L recording 'technique' is doing something very bizarre when putting down the DXD track: I'm looking at the Britten, Simple Symphony DXD track, and a half sample rate, ie. 176.2kHz, warble tone or whatever, is riding along, through the whole track. This goes up and down in amplitude, rising to only -40dB down at its worst! What the hell is that doing there?! This alone must do something to the processing, replay chain; perhaps because it's adding some sort of sparkle perhaps, by stimulating a distortion artifact??

Frank

[scott wurcer]

Originally Posted by SY

According to the reference, it was more like 1940.

True, that 1940 reference looks pretty straight to the point. I wish I had free access to the non-IEEE journals I would have found more interesting history. That one would have ended this discussion a long time ago.