Amplifier distortions - what, and how much are audible

[highfigh]

Okay, that was kinda fun. My results line up with what they're saying about higher frequencies masking distortion. I could hear it most easily at 31 and 63 hz.

I would recommend testing first thing in the morning, before the day's noise is able to raise someone's hearing threshold.

Testing for something like this is difficult the first time- we don't know what to listen for. I went in for a hearing test and asked to be re-tested at certain frequencies- I heard the tones at a lower level the second time.

 

[3db]

My results. It was obvious to me at -24db but then it got really hard to distinguish. This is my 1st ever listening test in this vain. I have my laptop connected to my system in the bedroom and I chose 6" drivers running the AVR in Pure Direct mode.

 

[PENG]

I did try the klippel test but started getting impatient and kinda rushed through the last few tests. -21 they said, which is a li'l embarrasing? I dunno. With a little more practice and maybe some headphones I know I could do better.

View attachment 45455

haha I warned you about patience! If you take the time you I am sure you will do better, Steve81 did very well, but still only score 42, I got 36 the first time, rush a little too in the end but not so much. Even with such low score, it apparently was high enough to be thought of as a trained listener (go figure!!). I chose a different song than Steve81's, not sure what difference it would have made.

Thanks again for participating.

 

[PENG]

View attachment 45469

My results. It was obvious to me at -24db but then it got really hard to distinguish. This is my 1st ever listening test in this vain. I have my laptop connected to my system in the bedroom and I chose 6" drivers running the AVR in Pure Direct mode.

I used my desktop system, also choose 6" driver, but my speakers was powered via a cheap passive subwoofer's filtered line output so the resolution sort of suffer a little, and that's the excuse I am sticking to.

 

[PENG]

My results. It was obvious to me at -24db but then it got really hard to distinguish.

Hard to distinguish? That would be for people like use but I bet for those who could hear "night and day" kind of difference between two seemingly well spec'd and measured amps.. Remember eargiant, wonder why he stopped posting here??

 

[Steve81]

Just for reference...

-10dB = 31.6%
-20dB = 10.0%
-30dB = 3.16%
-40dB = 1.0%

 

[AcuDefTechGuy]

-21 they said, which is a li'l embarrasing?
View attachment 45455

You should be embarrassed. I got a -100dB.

Just kidding. I got a -20dB on my iPad Pro.

 

[Pogre]

You should be embarrassed. I got a -100dB.

Just kidding. I got a -20dB on my iPad Pro.

I was using my speakers and sitting 15' away. I'm tempted to retry it with my earbuds. They're not great buds but they're not terrible. I think I could do a lot better with them. Or if I got a lot closer to my speakers. OR... my system sucks and isn't resolving enough to be able to hear the distortion!

 

[Steve81]

For my run I did use a pair of Sennheiser Momentum over ear phones on my laptop.

I just tried it again using only speakers on my iPad and scored -24dB. Was also more difficult since I could only do a single play through of each sample for whatever reason.

 

[PENG]

In my search in the past on related topics, I read about something Peter Walker allegedly had said so I just did a search and found this one:

Interview with Quad's Peter Walker in 1978 (theartofsound.net), in the first post, it claimed that:

".....the legendary Quad II's were designed and built without being listened to, except for nasty noises in extremis...

The poster did include a Geocities link to the original interview:

https://geocities.restorativland.org/ResearchTriangle/Lab/6722/pwint1.txt

in which you can see that PW supposedly said in the interview:
The part I highlighted bold, in big red fonts were the points he allegedly made that I could have made myself!

@TLS Guy , do you believe, or know that the linked interview with Peter Walker is from a credible source?

"TAA: Have you any opinions you'd share on the relative merits of distortion tests,
such as harmonic, two-tone IM, transient IM, or slew rate limiting, as clues to
amplifier quality?

PW: An amplifier should, within its limits of voltage and rate of change of voltage,
(which is slew rate limiting) if you keep within those two it should be very much
better than any program material. These are the things that are measured at .01
per cent or .05 per cent. But what is listened to is usually a program with 2 or 3
per cent distortion in the first place. That's the least you can get on records,
tapes, and such things. Listening tests are usually not done in this region of .01
percent distortion. I'm quite convinced within that range the amplifier is just as
perfect as you like to make it. It's quite possible to put 50 amplifiers in cascade,
each one into a load, potted down into the next one, and to listen to the 50th one
or to listen to the first one, and the sound will be virtually the same. So I think you
can make an amplifier just as good as you like, and no more different than a
piece of wire. But where they vary, when these tests are done, are a whole lot of
areas. To start with, you can compare one amplifier with a bass cut-off of 20 Hz
and another one that goes right down to DC. If you've got a program with a bit of
fluffing going on at 5 Hz or so, the speaker cone in one case will be moving, and
in the other case it won't be moving, so the sound from the speaker will be
different. This isn't really a condemnation of the amplifier, it's that they shouldn't
have this 5 Hz stuff there in the first place. So if you compare an amplifier with a
straight wire, you've really got to make the straight wire have the same
bandwidth as the amplifier, and the same terminating impedance as the
amplifier. Once you do all these things, then the amps will be just as good as the
straight wire. The peripheral effects are what get people into trouble. You can
see why you find these differences in amplifiers. You can always find them. If
people test two amplifiers and say, "These sound different," there's no magic in
it. Spend two days, maybe a whole week in the lab, and you find out exactly why
they're different and you can write the whole thing down in purely practical,
physical terms. This is why these two sound different, and the cause is usually
peripheral effects. It is not really a case of good or bad amplifiers, it's that the
termination impedances are wrong, or something of that sort.

TAA: How do you rate the merits of listening tests to instrument tests?

PW: We designed our valve (tube) amplifier, manufactured it, and put it on the
market, and never actually listened to it. In fact, the same applies to the 303 and
the 405. People say, "Well that's disgusting, you ought to have listened to it."
However, we do a certain amount of listening tests, but they are for specific
things. We listen to the differential distortion - does a certain thing matter?
You've got to have a listening test to sort out whether it matters. You've got to do
tests to sort out whether rumble is likely to overload pickup inputs, or whether
very high frequency stuff coming out of the pickup due to record scratch is going
to disturb the control unit. But we aren't sitting down listening to Beethoven's
Fifth and saying, "That amplifier sounds better, let's change a resistor or two. Oh
yes, that's now better still." We never sit down and listen to a music record
through an amplifier in the design stage. We listen to funny noises, funny
distortions, and see whether these things are going to matter, to get a subjective
assessment. But we don't actually listen to program material at all."

 

[PENG]

For my run I did use a pair of Sennheiser Momentum over ear phones on my laptop.

I just tried it again using only speakers on my iPad and scored -24dB. Was also more difficult since I could only do a single play through of each sample for whatever reason.

Steve, if the test sample music was done with the typical kinds of distortions produced by amps instead of loudspeakers, how much difference do you think it would make, just ball park of course. I couldn't find anything that provides some kind of correlation/comparison between the two, but I thought as a writer yourself, you might have..

For reference, there is one on loudspeaker (with some hard numbers) but we need one on amplifiers, for an apple to apple (or almost) comparison:

Human Hearing - Distortion Audibility Part 3 | Audioholics

 

[Steve81]

Steve, if the test sample music was done with the typical kinds of distortions produced by amps instead of loudspeakers, how much difference do you think it would make, just ball park of course.

Ballpark, using some gross generalizations and the old Emotiva XPA-2 as a foil to the speaker in the link for a THD comparison...



If we ignore the magnitude of the distortion and just focus on the relative level of the THD products, a couple things do pop out. The loudspeaker's distortion is dominated by 2nd and 3rd harmonics, while the XPA-2's higher even order harmonics are readily apparent. If we magically jacked up that distortion profile from its real world level to compare with loudspeaker distortion, I'd guess it would sound worse...maybe even significantly so.

One other factor that comes to mind is distortion vs frequency for speakers and amps. Loudspeakers obviously will struggle far more at the low end, while amps tend to see distortion rise at the top end (from what I've seen at least).

Given those two profiles for weighting our THD, I'd lean towards the speaker as being preferable. Imagine jacking up the Onkyo's 20V distortion to the point where the graph starts at 1% or more instead of 0.01% to better compare with the magnitude of loudspeaker distortion. Better to sh*t the bed on the low end where our hearing is less sensitive and be relatively clean through the rest of the range IMO.

 

[3db]

I was using my speakers and sitting 15' away. I'm tempted to retry it with my earbuds. They're not great buds but they're not terrible. I think I could do a lot better with them. Or if I got a lot closer to my speakers. OR... my system sucks and isn't resolving enough to be able to hear the distortion!

If knew what to listen for, maybe I would score higher as well. I have a pair of cheap Sony headphones so I will try them to see what gives. I was exposed to loud noises growing up on a farm and before knowing about hearing damage. If I still score the same with the Sonys, then I will adopt the attitude of ignorance is bliss which really opens the market for me!!!!!

 

[sweetness34]

That was fun! Not bad especially considering I was using some Bose bluetooth ear buds. Now I’m curious how I’d do on my actual AVR/speaker setup.

 

[AcuDefTechGuy]

Shouldn’t we use the same system that we listen to every day to test?

 

[Steve81]

Shouldn’t we use the same system that we listen to every day to test?

If you're trying to test the sensitivity of your ears to distortion. you want the cleanest playback you can get so the distortion intentionally introduced into the track isn't washed out by the distortion/noise of your rig.

 

[AcuDefTechGuy]

If you're trying to test the sensitivity of your ears to distortion. you want the cleanest playback you can get so the distortion intentionally introduced into the track isn't washed out by the distortion/noise of your rig.

I agree if we’re just testing our hearing acuity.

I thought we’re trying to see if we could hear THD+N in the real world environment.

For example, why should everyone care about THD+N of -100dB if we can’t even hear THD+N of -20dB in the real world environment with real speakers and amps and music, even in an extremely quiet room?

 

[highfigh]

In my search in the past on related topics, I read about something Peter Walker allegedly had said so I just did a search and found this one:

Interview with Quad's Peter Walker in 1978 (theartofsound.net), in the first post, it claimed that:

".....the legendary Quad II's were designed and built without being listened to, except for nasty noises in extremis...

The poster did include a Geocities link to the original interview:

https://geocities.restorativland.org/ResearchTriangle/Lab/6722/pwint1.txt

in which you can see that PW supposedly said in the interview:
The part I highlighted bold, in big red fonts were the points he allegedly made that I could have made myself!

@TLS Guy , do you believe, or know that the linked interview with Peter Walker is from a credible source?

"TAA: Have you any opinions you'd share on the relative merits of distortion tests,
such as harmonic, two-tone IM, transient IM, or slew rate limiting, as clues to
amplifier quality?

PW: An amplifier should, within its limits of voltage and rate of change of voltage,
(which is slew rate limiting) if you keep within those two it should be very much
better than any program material. These are the things that are measured at .01
per cent or .05 per cent. But what is listened to is usually a program with 2 or 3
per cent distortion in the first place. That's the least you can get on records,
tapes, and such things. Listening tests are usually not done in this region of .01
percent distortion. I'm quite convinced within that range the amplifier is just as
perfect as you like to make it. It's quite possible to put 50 amplifiers in cascade,
each one into a load, potted down into the next one, and to listen to the 50th one
or to listen to the first one, and the sound will be virtually the same. So I think you
can make an amplifier just as good as you like, and no more different than a
piece of wire. But where they vary, when these tests are done, are a whole lot of
areas. To start with, you can compare one amplifier with a bass cut-off of 20 Hz
and another one that goes right down to DC. If you've got a program with a bit of
fluffing going on at 5 Hz or so, the speaker cone in one case will be moving, and
in the other case it won't be moving, so the sound from the speaker will be
different. This isn't really a condemnation of the amplifier, it's that they shouldn't
have this 5 Hz stuff there in the first place. So if you compare an amplifier with a
straight wire, you've really got to make the straight wire have the same
bandwidth as the amplifier, and the same terminating impedance as the
amplifier. Once you do all these things, then the amps will be just as good as the
straight wire. The peripheral effects are what get people into trouble. You can
see why you find these differences in amplifiers. You can always find them. If
people test two amplifiers and say, "These sound different," there's no magic in
it. Spend two days, maybe a whole week in the lab, and you find out exactly why
they're different and you can write the whole thing down in purely practical,
physical terms. This is why these two sound different, and the cause is usually
peripheral effects. It is not really a case of good or bad amplifiers, it's that the
termination impedances are wrong, or something of that sort.

TAA: How do you rate the merits of listening tests to instrument tests?

PW: We designed our valve (tube) amplifier, manufactured it, and put it on the
market, and never actually listened to it. In fact, the same applies to the 303 and
the 405. People say, "Well that's disgusting, you ought to have listened to it."
However, we do a certain amount of listening tests, but they are for specific
things. We listen to the differential distortion - does a certain thing matter?
You've got to have a listening test to sort out whether it matters. You've got to do
tests to sort out whether rumble is likely to overload pickup inputs, or whether
very high frequency stuff coming out of the pickup due to record scratch is going
to disturb the control unit. But we aren't sitting down listening to Beethoven's
Fifth and saying, "That amplifier sounds better, let's change a resistor or two. Oh
yes, that's now better still." We never sit down and listen to a music record
through an amplifier in the design stage. We listen to funny noises, funny
distortions, and see whether these things are going to matter, to get a subjective
assessment. But we don't actually listen to program material at all."

I bet that if someone were to post this in a fancy cable discussion, every response would be "Who?". Then, they would dump all over whoever posted it because of their source.

That comment about low frequencies is something that needs to be remembered- extremely low frequencies can modulate other frequencies. The effect is similar to what happens when someone on one side of a spinning fan blade speaks to someone on the other side.

 

[highfigh]

That modulation is especially problematic when the system doesn't use a subwoofer- play pipe organ music with extremely low bass pedals and listen to the mid-bass as an example.

 

[PENG]

I agree if we’re just testing our hearing acuity.

I thought we’re trying to see if we could hear THD+N in the real world environment.

For example, why should everyone care about THD+N of -100dB if we can’t even hear THD+N of -20dB in the real world environment with real speakers and amps and music, even in an extremely quiet room?

Right, but keep in mind in a studio environment, using the best available electronics and loudspeakers you may be able to score higher than Steve81, but then it is still just -42 dB!!

So I think we can probably agree claims of night and day difference between a musical Arcam AVR/AVP and a clinical Yamaha AVR/AVP, or an ATI flagship amp vs the often trashed internal amp of even a flag ship AVR must be due to reasons other than those directly related to the said DUTs (devices under test).

As Peter Walker allegedly had said in the interview I linked earlier (still hoping @TLS Guy will confirm credibility of that interview):

An amplifier should, within its limits of voltage and rate of change of voltage,
(which is slew rate limiting) if you keep within those two it should be very much
better than any program material. These are the things that are measured at .01
per cent or .05 per cent. But what is listened to is usually a program with 2 or 3
per cent distortion in the first place. That's the least you can get on records,
tapes, and such things. Listening tests are usually not done in this region of .01
percent distortion. ...................................................................................................If
people test two amplifiers and say, "These sound different," there's no magic in
it. Spend two days, maybe a whole week in the lab, and you find out exactly why
they're different and you can write the whole thing down in purely practical,
physical terms. This is why these two sound different, and the cause is usually
peripheral effects. It is not really a case of good or bad amplifiers, it's that the
termination impedances are wrong, or something of that sort.

Coming from the founder of Quad Electroacoustics and the one attributed with the famous hifi quote "the perfect amplifier is a straight wire with gain", it is both surprising and unsurprising.

Back to your point, I supposed it is reasonable to aim for 0.05 to 0.01% even when 0.1 to 1 % may be all that matters. It is not totally unlike if you feel a couple of million is all you would ever spend post retirement based on your desired life style, yet you still won't consider it good enough unless you have saved up 5 millions.