Why hardly any of us have truly clean deep bass.. - Page 2 - AVS Forum
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post #31 of 33 Old 09-23-2013, 10:50 AM
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Quote:
Originally Posted by shadyJ View Post

I would say cleanly reproduced bass is that which has no audible distortion, that is, no audible sound which is not in the recording.

It turns out that the listening task associated with hearing distortion is not that simple.

Instead of trying to detect an audible sound that is not in the recording, your task may be to detect a minor level shift in a sound that is already in the recording.

Lets say that the recording contains a organ pedal note whose fundamental frequency is say 40 Hz. We know that:

(1) The recorded real world organ note is composed of both the fundamental and a number of harmonics
(2) The fundamental is far weaker than some of its harmonics especially the second and third harmonics.

The recording of the organ pedal note might have 20% fundamental, 60% second harmonic, and 20% remaining harmonics.

If there is 10% second order distortion at the fundamental frequency or 40 Hz, then the second harmonic created by the distortion is 2% or 10% of 20%. Add that to the second harmonic in the recording, and we are now trying to detect the difference between roughly 60% second harmonic and 62% second harmonic. That is a mere 0.3 dB difference. At 80 Hz, a 0.3 dB dB difference is difficult or impossible to hear because the ear just isn't so sensitive to differences at low frequencies.
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post #32 of 33 Old 09-23-2013, 11:12 AM - Thread Starter
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Quote:
Originally Posted by arnyk View Post

It turns out that the listening task associated with hearing distortion is not that simple.

Instead of trying to detect an audible sound that is not in the recording, your task may be to detect a minor level shift in a sound that is already in the recording.

Lets say that the recording contains a organ pedal note whose fundamental frequency is say 40 Hz. We know that:

(1) The recorded real world organ note is composed of both the fundamental and a number of harmonics
(2) The fundamental is far weaker than some of its harmonics especially the second and third harmonics.

The recording of the organ pedal note might have 20% fundamental, 60% second harmonic, and 20% remaining harmonics.

If there is 10% second order distortion at the fundamental frequency or 40 Hz, then the second harmonic created by the distortion is 2% or 10% of 20%. Add that to the second harmonic in the recording, and we are now trying to detect the difference between roughly 60% second harmonic and 62% second harmonic. That is a mere 0.3 dB difference. At 80 Hz, a 0.3 dB dB difference is difficult or impossible to hear because the ear just isn't so sensitive to differences at low frequencies.

I see. Interesting stuff, thanks for the explanation. I guess harmonic distortion only makes a big difference when there is lots of it or when the original content just doesn't have extra harmonic material.

I take it I am the only one who likes to sit back after a hard day of work, pour myself a glass of Chardonnay, and put on a soothing 20 Hz sine wave for a few hours?
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post #33 of 33 Old 09-23-2013, 12:43 PM
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Interesting discussion so far. A couple thoughts on this. I don't have access to the full studies on audibility thresholds of distortion or the white papers on how the equal loudness curves were created, but from what I have found most of those studies were performed with headphones. IMO, "hearing" is only part of how we perceive low frequencies. We "feel" the bass in our bodies and depending on the room, we feel vibrations through the floor or furniture. Again IMO, taking that into account, will lower the thresholds and change the ELC curves at lower frequencies, but will vary depending on the room / environment.

And to expand on how in room measurements largely affect the distortion of a sub, here are some in room measurements of a single velodyne dd18. Even with the limiter kicking in, THD remains below 5% below 40hz. Unfortunately I don't have the outdoor measurements saved for direct comparison, but looking at the DD18+ on DB.com should give a general idea.



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