... Unusual music will give it fits, though, I suspect.
I'm getting an impression from you and JJ that loudness compensation EQ has to vary as the signal level varies within a given musical performance, and I find that hard to accept. If it is in fact the case, I have some learning to do. I'll have to get Holman's paper that you referenced.
... Take any equal loudness contour curve family and re-graph the data for any bass frequency as a gain differential between 1khz and that frequency. You'll see the resulting graphs for lower frequencies are not straight lines, they are non-linear curves.
Quote from: dc2bluelight on 31 March, 2012, 12:19:04 PM... Take any equal loudness contour curve family and re-graph the data for any bass frequency as a gain differential between 1khz and that frequency. You'll see the resulting graphs for lower frequencies are not straight lines, they are non-linear curves.Is this the differential you refer to? At the 40 phon level, the differential between 1 KHz and 20 hz is about 60 dB. At the 60 phon level, the differential between 1 KHz and 20 hz is about 50 dB. At the 80 phon level, the differential between 1 KHz and 20 hz is about 40 dB.
From memory the actual differences above seem too high, but that's the general idea.
Phon F-M R-D ISO---- --- --- ---40 42 50 6060 26 41 5080 10 32 40
Phon F-M R-D ISO---- --- --- ---40 42 50 60=20 =16 =9 =1060 =26 41 50=20 =16 =9 =1080 10 32 40
This holds true within a dB or two for other phon levels, especially in the ISO curves. OK so far?
... Sorry, I don't have a convenient way to check your data for accuracy. But assuming it is (accurate), what's your point?
Your example assumes that all stimulus within the entire spectrum start out at a perceived equal loudness relative to each other. But what, for example, if a bass note were intended to be 10dB below a mid-band note? At the original level, all is well, but if you alter the play level, you'll find that the two notes land on entirely different theoretical curves. And even that example is too static to be realistic.
But the equal-loudness contour curves do not represent the actual correction needed, because they are not correction curves at all, they are graphs of stimuli level required for perceived equal loudness. The actual correction curve must be derived from a known original reference level, and the new play level of each independent stimulus frequency, and the predicted differential in ear/brain response shown by the contours.
Note: you can't apply a single curve to the spectrum, you have to correct for the level of each frequency because (and this is the key) the ear/brain system is non-linear to a different degree for each frequency below mid-band.
So, for proper loudness compensation you need to know:1. The acoustic original level (at the time of recording)2. The new acoustic level during playback of each frequency or group below 1KHz (actually, 400Hz would work as well)3. The amount of correction needed for each frequency to re-establish spectral balance for playback at the new level considering its specific moment to moment acoustic level.
... The only volume setting at which a fixed, non-variable correction curve would be right would be that which results in the exact acoustic level of the original performance, at the original listening position. In other words, the level at which no loudness compensation is required.
... So, just because I'm running out of gas on this, here's the "agree to disagree" statement: feel free to build up your favorite curve set in a DSP, and give it a whirl. Make it adjustable using non-variable curves. Use the old one-knob or two, or three, or no knobs. Tweak it by ear, RTA, FFT, or fuzzy clustering. One of the nice things is, today, it's not so big a deal to do that, even if you do prefer to ignore the research. Who knows? You just might be thrilled with your result! And that, I would have to say, will make it valid for you. But you may want to grab a few of those loudness research papers and look them over. At very least, you'll have a cure for insomnia.
I'd iterate, one last time, three points:
The above three points should be enough to send anyone interested in loudness comp to the library to see what the Loudness Jedi have learned over the years. I'd just hate to see anyone try to re-invent the square wheel (even in DSP) when experts have already agreed it needs to be round.