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Audibility of low frequency distortion

dougi

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I've pointed this out a few times when this graph has been posted, so sorry to repeat myself again, but it should be clarified (since Axiom kind of glosses over this point) that the average spectrum of music is far from flat.

So when Axiom says that the music was playing at, say, 86dB, that certainly doesn't mean that the level of the music was 86dB in the treble.

In fact, typical spectra of music look something like this:

View attachment 97861

Which interestingly is a very similar shape to the threshold curve that Axiom generated from their tests.
That is a very good point. So the Axiom graph should really be weighted by something like your curve above? Which would imply that, for example, if Axiom showed a min distortion detection level of around -35dB wrt average music level at 10 kHz as detectable, then in reality the % distortion wrt music level at 10kHz is a fair bit higher?
 

andreasmaaan

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That is a very good point. So the Axiom graph should really be weighted by something like your curve above? Which would imply that, for example, if Axiom showed a min distortion detection level of around -35dB wrt average music level at 10 kHz as detectable, then in reality the % distortion wrt music level at 10kHz is a fair bit higher?

That's more or less how I interpret it. It's not possible to know for sure of course. And it must also be noted that the dynamic range of music will vary a lot with frequency (tending to be higher at higher frequencies, even if it was only 5 or 6dB overall according to the Axiom article).

It's also worth noting that masking of a 10kHz tone, for example, is not equivalent to masking of harmonic distortion of a 10kHz fundamental, but rather to masking of 2nd harmonic distortion of a 5kHz fundamental, 3rd harmonic distortion of a 3,333kHz fundamental, and so on.

So, although it's a very interesting test, and does seem to demonstrate quite well in general that masking is more effective than commonly assumed (especially where the signal is complex, as in music), I would still tend to look to more traditional masking studies (those that test for threshold of a maskee in the presence of a narrow-band noise masker or a pure tone masker) for a more rigorous indication of masking thresholds.
 

ctrl

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This one of test by Axiom is interesting in that is describes and audibility curve vs frequency. link
Thanks for the link.

The results with music/noise as masker fit nevertheless quite well to the so far shown results of studies.

Even if the 92dB sound pressure levels ("average 92 dB SPL playback level") were not specified exactly, the hearing limit for the interfering signal in the frequency range of 300-100Hz with an average of 15-30% is in the range one would expect - for such a "wide" masker.
 

dougi

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That's more or less how I interpret it. It's not possible to know for sure of course. And it must also be noted that the dynamic range of music will vary a lot with frequency (tending to be higher at higher frequencies, even if it was only 5 or 6dB overall according to the Axiom article).

It's also worth noting that masking of a 10kHz tone, for example, is not equivalent to masking of harmonic distortion of a 10kHz fundamental, but rather to masking of 2nd harmonic distortion of a 5kHz fundamental, 3rd harmonic distortion of a 3,333kHz fundamental, and so on.

So, although it's a very interesting test, and does seem to demonstrate quite well in general that masking is more effective than commonly assumed (especially where the signal is complex, as in music), I would still tend to look to more traditional masking studies (those that test for threshold of a maskee in the presence of a narrow-band noise masker or a pure tone masker) for a more rigorous indication of masking thresholds.

Yes I fully concur. What I find interesting is this is a really tricky balancing act for ASR and others focussed on objectivity. Amir can measure a lot of parameters but then, because of the psycho-acoustic grey areas that still exist it is difficult to be definitive about what is audible and what is not. Hence sometimes erring on the pessimistic in terms of acceptable speaker distortion for example. I imagine a lot of pretty conclusive research has been done or how else could I have happily been listening to ABC Jazz last night at 80kbps AAC plus via terrestrial digital radio?
 

andreasmaaan

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Yes I fully concur. What I find interesting is this is a really tricky balancing act for ASR and others focussed on objectivity. Amir can measure a lot of parameters but then, because of the psycho-acoustic grey areas that still exist it is difficult to be definitive about what is audible and what is not. Hence sometimes erring on the pessimistic in terms of acceptable speaker distortion for example. I imagine a lot of pretty conclusive research has been done or how else could I have happily been listening to ABC Jazz last night at 80kbps AAC plus via terrestrial digital radio?

Completely agree with you there :)

Which ABC Jazz are you talking about? Not ABC Australia by any chance??
 

dougi

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Completely agree with you there :)

Which ABC Jazz are you talking about? Not ABC Australia by any chance??
Yeah ABC Australia. Most of my career has been in broadcasting transmission and compression so I had the pleasure of being a key part of introducing digital radio (and TV) here. Not in broadcasting any more, which is probably a good thing given it's rapidly dwindling importance in the eyes (and ears) of most consumers.
 

andreasmaaan

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Yeah ABC Australia. Most of my career has been in broadcasting transmission and compression so I had the pleasure of being a key part of introducing digital radio (and TV) here. Not in broadcasting any more, which is probably a good thing given it's rapidly dwindling importance in the eyes (and ears) of most consumers.

Nice to hear your story :) I used to listen to ABC Jazz (and many other ABC stations) frequently when l lived in Aus. That was mostly in the car via old-fashioned AM/FM radio. Fond memories. I should stream these stations now that it's possible from anywhere (I'm in Germany now). Would be interested to hear about your former work if you'd care to tell more...
 

restorer-john

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Would be interested to hear about your former work if you'd care to tell more...

I would also be very interested. Maybe start a thread about your time in broadcasting with ABC Australia? :)

We had a thread started by @Frank Dernie about his time with Garrard which was fascinating.
 
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