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Over in the "Need for a general statement thread" a discussion sprang up about audible thresholds for non-linear distortion. I mentioned a couple of studies which appear to be very thoughtfully planned and well-executed, which examined aspects of this topic in different ways.
The first is by de Santis from 2007 and is called Perception & Thresholds of Nonlinear Distortion using Complex Signals.
Here, the author used software to introduce varying kinds and degrees of nonlinear distortion to music signals, and then had subjects undergo trials to try to determine which subjective reports correlated best with 4 different distortion metrics: the old and simple THD, IMD, and then the newer and more compex DS and Rnonlin metrics. Low correlations were found in the cases of THD and IMD, while impressively high correlations were found with the newer metrics. The speculated reasons for this were to do with THD and IMD's failures to take into account various aspects of human auditory processing, most importantly the relationship between critical bands in the auditory system and masking, but also other aspects. Although there is no discussion or experimentation in terms of absolute thresholds, it's a very interesting read.
The second study is by Robert-Eric Gaskell and is called Subjective and Objective Evaluation of Distortion in Analogue Electronics.
Here, the author digitally modelled non-linearities in capacitors and opamps and then set up controlled trials to determine audibility thresholds for the modelled distortions. There's a lot going on in this study but the most interesting conclusion from my point of view was this one:
"In the listening tests performed for this dissertation, participants were able to detect levels of capacitor distortion as low as 0.002% THD+N and levels of opamp distortion as low as 0.005% THD+N." Note, however, that the methodology used is complex and therefore this statement needs to be read in the context of the study as a whole.
Hope these provide food for thought.
Andreas
The first is by de Santis from 2007 and is called Perception & Thresholds of Nonlinear Distortion using Complex Signals.
Here, the author used software to introduce varying kinds and degrees of nonlinear distortion to music signals, and then had subjects undergo trials to try to determine which subjective reports correlated best with 4 different distortion metrics: the old and simple THD, IMD, and then the newer and more compex DS and Rnonlin metrics. Low correlations were found in the cases of THD and IMD, while impressively high correlations were found with the newer metrics. The speculated reasons for this were to do with THD and IMD's failures to take into account various aspects of human auditory processing, most importantly the relationship between critical bands in the auditory system and masking, but also other aspects. Although there is no discussion or experimentation in terms of absolute thresholds, it's a very interesting read.
The second study is by Robert-Eric Gaskell and is called Subjective and Objective Evaluation of Distortion in Analogue Electronics.
Here, the author digitally modelled non-linearities in capacitors and opamps and then set up controlled trials to determine audibility thresholds for the modelled distortions. There's a lot going on in this study but the most interesting conclusion from my point of view was this one:
"In the listening tests performed for this dissertation, participants were able to detect levels of capacitor distortion as low as 0.002% THD+N and levels of opamp distortion as low as 0.005% THD+N." Note, however, that the methodology used is complex and therefore this statement needs to be read in the context of the study as a whole.
Hope these provide food for thought.
Andreas
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