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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: RE: "In addition the listeners need to be qualified, trained and their qualification and training proven." posted by Tony Lauck on May 28, 2010 at 12:13:35:
Not only this, repeatable experiments at the limit of detection (LOD) need to be carried out as well as a limit of quantification (LOQ) if possible. With human subjects as the "detectors" of the phenomena this is difficult at best.
In order to prove that a system is capable detecting and resolving what it is proposed to be detecting/resolving it must pass at least a rudimentary system suitability test and/or basic validation.
What this generally involves is the following:
For a qualitative analysis similar items must be tested together to determine if they are separable from each other (in chromatography are two compounds separable or do the come out as only one peak). For audio this could be a sensitivity to different kinds of distortion and not just one kind. Determining which listeners are sensitive to different distortions and if they can distinguish between different kinds of distortion.
An element to be detected that is tested at different levels (in chemistry this would be at different concentrations for a quantitative analysis) in order to establish if the response to differing levels is linear and if it is linear over how wide of a range. For audio this could taking the above distortions and supplying them in progressively lower levels until they are no longer detectable. Some way of giving a quantitative numbering to what they hear needs to be developed so that linearity or lack thereof can be evaluated.
Accuracy would need to be evaluated after training. This could be by assigning each level of a particular distortion with a number and when the individual hears that level they can correctly give it the right level number. They should have to be able to do this with all distortions presented as part of the validation. If a signal is given that is in-between levels then they should be able to determine that it is in-between two levels, etc.
Once this has been shown then the reproducibility of the detection must be shown. This will establish the variance of an individual "detector" as well as establishing the variance between different individuals to different distortions at different levels. As you can see this could easily become a multi-variate problem...and non-linear at that.
Good luck calibrating and qualifying human listeners, it is quite probable that the intra and inter person variance will be so high that meaningful statistical analysis will not be possible. Maybe we get lucky and one individual is so good that he/she can be used for a study, which will of course only be valid within the range of that individual's validated hearing range.
It may be that the most repeatable and accurate listener is not the one with the highest sensitivity to certain distortions and that their LOD is not as good as others who are less predictable.
In analytical science, we always know there are things there that we cannot detect. For some things that is irrelevant but for others it doesn't mean there are not real consequences. Take detection of heavy metals, for example. There is essentially no safe levels of lead and mercury and once upon a time analytical science was unable to detect levels that today would be considered unacceptable. Now, the detection limits are sub parts per billion (ppb) and that is STILL considered not safe. This means that there are undetected levels that may still impact human health.
Audio has a similar conundrum, distortion levels of some gear are vanishingly low according to sensitive test instruments; however, there still seems to be an impact on what we hear. Is that because there are some kinds of distortions for which there is no "safe" levels??
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Follow Ups
- RE: "In addition the listeners need to be qualified, trained and their qualification and training proven." - morricab 09:25:53 06/02/10 (0)
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