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Steve G incites new rage in objectivists!

cjfrbw

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SIY

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Jan Didden (former publisher of Linear Audio and current Technical Editor of AudioXpress) is here with me this week on his yearly visit. While he's here, besides our usual alcohol consumption, we've been doing a lot of measurement of all sorts of things (power supplies, loudspeakers, preamplifiers...). And when things look funny, as odd as this seems, we do control measurements to determine whether it's the DUT or operator stupidity. So far, it's run 9:1 in favor of the latter.

And that's the difference between duffers and folks who know what they're doing. But distinguishing that makes a poor audiophile argument. Best to assume that no one really can do measurements properly, or interpret them rationally. It gets more YouTube views.
 

andreasmaaan

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Some real classics buried in the comments:

1539368638243.png



1539368688527.png


And possibly my favourite from the Ministry of Sound fan:

1539368728032.png
 

oivavoi

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Jan Didden (former publisher of Linear Audio and current Technical Editor of AudioXpress) is here with me this week on his yearly visit. While he's here, besides our usual alcohol consumption, we've been doing a lot of measurement of all sorts of things (power supplies, loudspeakers, preamplifiers...). And when things look funny, as odd as this seems, we do control measurements to determine whether it's the DUT or operator stupidity. So far, it's run 9:1 in favor of the latter.

And that's the difference between duffers and folks who know what they're doing. But distinguishing that makes a poor audiophile argument. Best to assume that no one really can do measurements properly, or interpret them rationally. It gets more YouTube views.

Interesting. May I ask what kind of measurements it was that you got wrong, and what the source of the error usually was? Might be interested in case I ever get so foolish as to start measuring things myself...
 

SIY

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You have to promise not to laugh or to suggest that perhaps the Irish whiskey is a contributing factor.

There were many, but here's a couple examples:
Jan developed an interface for using sound cards as audio analyzers (I wrote a series of articles about this). His circuit has two interesting twist over the crude circuits I was using- it autoranges the input signal to keep it near the 2V sweet spot of most sound cards and it has a tracking notch filter for a 1kHz input so that if the frequency is off by a few Hertz, the notch adjusts. It seemed to work well, but we kept getting -110dB 3rd harmonic regardless of the range or where the notch filter was centered or the fundamental frequency. "Huh," he said, "maybe I need to change out the opamps..." After playing around a bit more, it suddenly occurred to me- I had been almost exclusively using the AP to generate digital outputs, using the analog generator to measure tube amps. In this case, I was using its analog generator for an ultra-low distortion op-amp-based circuit. So we did a baseline loopback measurement which showed... yep, -110dB 3rd harmonic. His Autoranger was working perfectly. I sheepishly went to the AP website and checked the APx525 distortion specs, which were, "-110dB typical." Oops.

We were doing noise measurements of his Silent Switcher, which is a module that plugs into a USB port and outputs +15, -15, and +3.3/5/6.5 (depending on a resistor setting). We of course did a baseline noise measurement with the probe leads shorted, then measured the +15 output, which showed more noise than baseline. Fine. Then we ran the -15, and its noise spectrum tracked the +15 almost perfectly. "The +6.5V doesn't have a post regulator, so it should be noisier," he explained. And when we tested it, its noise spectrum overlaid the +15 and -15 curves. That's not right (because we understand what regulator noise spectra should look like), so I grabbed my bench voltmeter and checked the outputs. Yes, they were all zero! He furiously started checking connections, changing jumpers, then suddenly yelled, "SHIT! I installed the USB connector on the wrong side of the board!" A few minutes of desoldering and resoldering later, the voltages were right and the noise spectra made sense (by the way, this is a superb power supply).

Later when I have time, I'll talk about how I figured out the inadvertently bad gating selections made the loudspeaker frequency response measurement plausible but totally wrong. And how we figured out that my clip leads were hooked to the wrong BNC jacks of the AP. But at the moment, we have some drinking to do because it's 5 o'clock somewhere.
 
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Thomas savage

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You have to promise not to laugh or to suggest that perhaps the Irish whiskey is a contributing factor.

There were many, but here's a couple examples:
Jan developed an interface for using sound cards as audio analyzers (I wrote a series of articles about this). His circuit has two interesting twist over the crude circuits I was using- it autoranges the input signal to keep it near the 2V sweet spot of most sound cards and it has a tracking notch filter for a 1kHz input so that if the frequency is off by a few Hertz, the notch adjusts. It seemed to work well, but we kept getting -110dB 3rd harmonic regardless of the range or where the notch filter was centered or the fundamental frequency. "Huh," he said, "maybe I need to change out the opamps..." After playing around a bit more, it suddenly occurred to me- I had been almost exclusively using the AP to generate digital outputs, using the analog generator to measure tube amps. In this case, I was using its analog generator for an ultra-low distortion op-amp-based circuit. So we did a baseline loopback measurement which showed... yep, -110dB 3rd harmonic. His Autoranger was working perfectly. I sheepishly went to the AP website and checked the APx525 distortion specs, which were, "-110dB typical." Oops.

We were doing noise measurements of his Silent Switcher, which is a module that plugs into a USB port and outputs +15, -15, and +3.3/5/6.5 (depending on a resistor setting). We of course did a baseline noise measurement with the probe leads shorted, then measured the +15 output, which showed more noise than baseline. Fine. Then we ran the -15, and its noise spectrum tracked the +15 almost perfectly. "The +6.5V doesn't have a post regulator, so it should be noiser," he explained. And when we tested it, its noise spectrum overlaid the +15 and -15 curves. That's not right Because we understand what regulator noise spectra should look like), so I grabbed my bench voltmeter and checked the outputs. Yes, they were all zero! He furiously started checking connections, changing jumpers, then suddenly yelled, "SHIT! I installed the USB connector on the wrong side of the board!" A few minutes of desoldering and resoldering later, the voltages were right and the noise spectra made sense (by the way, this is a superb power supply).

Later when I have time, I'll talk about how I figured out the inadvertently bad gating selections made the loudspeaker frequency response measurement plausible but totally wrong. And how we figured out that my clip leads were hooked to the wrong BNC jacks of the AP. But at the moment, we have some drinking to do because it's 5 o'clock somewhere.
I hereby charge you with being drunk in charge of a AP machine.
 

mansr

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He furiously started checking connections, changing jumpers, then suddenly yelled, "SHIT! I installed the USB connector on the wrong side of the board!"
One more reason to use SMD whenever possible.
 

SIY

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The whole board is SMD, but USB connectors (the square kind) tend to be through-hole for mechanical reasons. So of course, that was the one component he screwed up...:facepalm:
 

mansr

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The whole board is SMD, but USB connectors (the square kind) tend to be through-hole for mechanical reasons. So of course, that was the one component he screwed up...:facepalm:
USB connectors often have through-hole tabs for mechanical support. The electrical pins can be either through-hole or surface-mount. SMD is better for signal integrity since stubs and sharp corners can be avoided.
 

SIY

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The USB here is only used for power, so signal integrity is a non-issue. Jan feels that the SMD versions, despite the tabs, are just not as sturdy. And registration for hand mounting is more difficult.
 

mansr

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The USB here is only used for power, so signal integrity is a non-issue. Jan feels that the SMD versions, despite the tabs, are just not as sturdy. And registration for hand mounting is more difficult.
There any many variants available. I've found Amphenol/ICC USB connectors to be decent. For B type, I prefer the micro variety. The full-size is just too bulky.
 

Grave

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I am troubled by this ignoramus.

Sure, many people prefer low fidelity to high fidelity, but this makes no sense to me personally.

You do not have to be an engineer in order to understand measurements.

There is nothing inherently misleading about measurements.
 

Sal1950

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Audio has many problems. Steve is just one of them.
I hate the approach of name calling, it's so immature and grammar school level.
But the truth is that Steve is just an idiot. :mad:
 

amirm

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Funny this came up today as someone asked me to measure acoustic products and I told him that measurements there can be highly misleading. We have two ears and how we hear in a room is different in each ear. So one microphone can't measure the right things. In that regard, Steve is both right and wrong. He is right that in acoustics you have to darn well know what you are doing or you will totally draw the wrong thing.

He is wrong of course that measurements are misleading elsewhere. Strange that he thinks good measurements could bias someone's listening tests. How come he doesn't deal with that bias in his sighted testing?

As example of bad measuring devices he cites LP versus CD. LP sounds better many times because it has been mastered differently. It doesn't sound better because it has worse specs than CD.

I bet if I digitized an LP and then did an AB between that LP on the same system and a CD blind, he could not tell them apart or have any preference for the LP.
 

SIY

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So one microphone can't measure the right things.

It can if you don't mind moving it around (and understand measurement technique- not a trivial matter!). And the DUT as well.

Interpretation is a bit trickier, but we have a lot of literature to guide in that, not the least of which is work by Toole and Geddes.
 

Blumlein 88

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snippage.............

I bet if I digitized an LP and then did an AB between that LP on the same system and a CD blind, he could not tell them apart or have any preference for the LP.

I've done this informally. And you know what? Some people could detect 44 khz, but not 48 khz or 88 khz. I suspect the moving coil in use is the reason. I know it has a resonance around 22 khz.
 
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