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Are Electronic Amplifiers a Solved Problem ??

Wes

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#1
How do we know that the SINAD differences ASR exposes are inaudible in amps & pre-amps?

Or.. what amount of SINAD would constitute a JND - assume top quality speakers & source material...
 

sergeauckland

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#2
Tests done as far back as the 1950s indicated that around 1% distortion was inaudible on programme material (speech or music) so aiming for 0.1% at all levels and frequencies was felt to be comfortably inaudible.

I've not seen any evidence that this is inadequate so a -60dB level for distortion is fine.
Bear in mind that analogue tape had 3% distortion, and around -60dB noise at best, with around 0.1% W&F so that puts into perspective all those vintage recordings so praised for their quality.
S
 
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Wes

Wes

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Thread Starter #3
cites?

also, was that THD, or what?
 

Fluffy

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#4
SINAD is basically THD+N, which is a combination of all distortions and noise in the signal. Testing audibility of noise is simple – if you hear a hiss, you hear the noise. If you don't hear it, then the noise is not audible.

You can find out for yourself how much distortion can you detect with this test: https://www.audiosciencereview.com/forum/index.php?threads/distortion-listening-test.8152/

Hearing under -60 db of distortions is practically impossible, and most people managed to hear no lower then -40 db. -60 db is 0.1%, so it's safe to say that THD of under 0.1% is nothing to worry about.
 

Blumlein 88

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#5
This points out why I don't like Sinad. -60 db Sinad all noise is clearly audible. -60 db all distortion almost surely inaudible. You need to look at distortion and noise separately. You also need to examine frequency response on it's own.

Flat enough response, low enough distortion and low enough noise then you are good.
 
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Wes

Wes

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Thread Starter #6
ok, so we need a phase plot or scatterplot with THD on one axis and Noise on the other

then, there would be an indifference curve drawn, with a rel. flat area at about 60 dB down on the Noise axis...
 

sergeauckland

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#7
cites?

also, was that THD, or what?
As for citations, I can't put my finger on any right now, it's what I was taught back in the 1960s. Yes, it would be THD, and it referred to audibility on speech and music, not test tones.

S
 

Blumlein 88

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#9
On this question I've responded elsewhere, that THD of -70 db or better, IMD of -80 db or better and noise of -100 db or better should do the trick.

Frequency response should be +/- .1 db from 20 hz to 20 khz.
 

Inner Space

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#10
Probably astonishing SINADs are inaudible, but based on my experience of e.g. Benchmark, the same kind of meticulous design attention also shows up in channel separation, which I have found to be audible. I'm not sure where and when the accepted threshold figure for separation was derived. Was it early in the stereo era? Maybe it should be revisited.
 

sergeauckland

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#11
Probably astonishing SINADs are inaudible, but based on my experience of e.g. Benchmark, the same kind of meticulous design attention also shows up in channel separation, which I have found to be audible. I'm not sure where and when the accepted threshold figure for separation was derived. Was it early in the stereo era? Maybe it should be revisited.
20dB separation is sufficient for decent stereo placement, and any electronics does a lot better, so that leaves loudspeakers and rooms. Any idea what the separation in-room actually is?
S
 

Wombat

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#12
Read this and consider if (I'm assuming the OP is referring to audio) amplifiers need to be a problem:

Resolution.

AF is a doddle in the amplifier design zoo.
 
Last edited:

mhardy6647

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#13
20dB separation is sufficient for decent stereo placement, and any electronics does a lot better, so that leaves loudspeakers and rooms. Any idea what the separation in-room actually is?
S
Thus (e.g.,) Mr. Polk and his Stereo Dimensional Array

Then

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1596456565542.png

1596456583734.png


and now (sans Polk himself, but still...)

1596456627229.png


I think some of us :) were surprised (not necessarily disappointed) that the current "SDA" implementation is strictly an analog solution, rather than fiddlin' and diddlin' with the signal in the digital domain.

For the record, I personally have never been a big fan of Polk's SDA loudspeakers -- but I do (still) quite like Polk's early (and very deliberately inexpensive) consumer loudspeaker products. I've owned and appreciated a pair of Polk's "Monitor Series Model 7A" loudspeakers since 1978.
 
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Wes

Wes

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Thread Starter #15
let's not get off topic into speakers.
 

valerianf

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#16
In the 80's there was a qualitative jump in quality when Japanese brands have provided new integrated amps with THD specified below 0.1%
Let us not get the AVR manufacturers do a regression: with nowadays components that are far better they can match the 80's evolution!
 

MakeMineVinyl

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#17
Bear in mind that analogue tape had 3% distortion, and around -60dB noise at best, with around 0.1% W&F so that puts into perspective all those vintage recordings so praised for their quality.
S
Not to nitpick, but 1950s - 1960s analog tape at normal operating level (185nWb) had distortion between about 0.6% and 1% distortion using the usual tape of the day, Scotch 111 or its equivalent. The level which produced 3% distortion was about 6-10dB above that, and this level is what was generally used for signal to noise specification, which was typically 55dB for half track 15ips. The CCIR equalization curve which is used in Europe suffered less low frequency distortion than machines in America which used the NAB curve. This is because the NAB curve specifies pre-emphasis on the low end by as much as 6dB which can cause more distortion with program material which has lots of low frequencies, like pipe organ.

The companies which are selling high-end tape copies today use the CCIR curve, thankfully.

Back to our regularly scheduled thread.......
 
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#18
The standard set of electronic measurements indicate that amplifiers for audio frequency material have achieved transparency. Same goes for DAC's. The problem is that while a spinorama speaker measurement set has .86 and more correlation to listener preference, for audio electronics no measurement set has the same predictive power in terms of listener preference.
 

sergeauckland

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#19
Not to nitpick, but 1950s - 1960s analog tape at normal operating level (185nWb) had distortion between about 0.6% and 1% distortion using the usual tape of the day, Scotch 111 or its equivalent. The level which produced 3% distortion was about 6-10dB above that, and this level is what was generally used for signal to noise specification, which was typically 55dB for half track 15ips. The CCIR equalization curve which is used in Europe suffered less low frequency distortion than machines in America which used the NAB curve. This is because the NAB curve specifies pre-emphasis on the low end by as much as 6dB which can cause more distortion with program material which has lots of low frequencies, like pipe organ
The companies which are selling high-end tape copies today use the CCIR curve, thankfully.

Back to our regularly scheduled thread.......
You're right about operating levels, except that most tape machines were used with VU meters, so peak levels were often if not always well above normal operating level as set on line up tone. A few machines, more broadcast than recording, were used with PPMs, so would have lower distortion, albeit at the expense of noise. Later, higher output tapes like Scotch 206 or Ampex Grand Master upped operating levels to 320nWb/m and even then, peak levels went higher as VU meters always under read.
Anyway, as you were!

S
 
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