John Kenny
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I know the "received wisdom" is that blind tests require volume matching to within 0.1dB for a valid test otherwise the "louder" device/track will be perceived as of better quality & not perceived as louder. My question is where are the blind test results which support this claim? Are there any blind test results with music as the signal (this is what we are talking about in most blind testing) that show level differences > 0.1dB are perceived differentially?
Now in my researching this topic I came across this Audioholics article which seems quite sensible in it's approach & does as survey of the research papers on the topic
In it a chart of research results over 60 years is given & the lowest JND is 0.25dB F.E. Toole and S. Olive, "The Modification of Timbre by Resonances: Perception and Measurements", JAES vol 36, # 3, March 1988, pp 122-142
The author states "Toole and Olive, on the other hand, in their 1988 study used pink noise for their acoustic signal source and determined that a 5 kHz resonance, with Q = 1 was just detectable at .25 dB." But later "The .25 dB figure quoted from the Toole & Olive research seems to contradict this (his JND of 0.75dB or 1dB), but consider the filter Q = 1. That's a pretty broad chunk of the audible spectrum over which that resonance exists. With the ear-brain combo performing an integration across that broad a portion of the audible spectrum than its easy to see how a large amount of acoustical energy is captured, leaving a change that small noticeable. However, pink noise is not real world and one thing my research has shown is that the hearing process reacts very differently to different types of sound; a .25 dB detectable difference using real music just isn't plausible and the research supports that."
He goes on to state "In this particular article, I settled on a minimum discernable difference dB value of .75 - 1.0. My experience has shown that this is what the average listener, under average listening conditions, listening to music played back through typical consumer-grade audio gear will be able to clearly identify - and do so repeatedly."
Now loudness is a psychoacoustic phenomena i.e intensity + auditory processing -> perception of loudness so some factors relating to this. The frequency filterbank (ERBs) that we split the sound into & analyse over is instrumental in how we perceive loudness. In other words, a single tone whose frequency falls into one filterbank, will be perceived as quieter than a wider band signal that spans more than one frequency filterbank, given that both are the same intensity (dB).
A consequence of this is that we are more sensitive to broadband noise intensity than to single tones & hence there is a curve of noise sensitivity called ITU-R 468 which defines our sensitivity to noise intensity & it is different to the Fletcher-Munson curves. here's the comparison which shows that we are more sensitive to noise @ 6KHz frequency than to a single tone at this frequency by > 12dB as can be seen here:
So, my questions again
- what evidence do we have that intensity mismatches of > 0.1dB will be perceived as quality issues with music signal
- what is the JND for amplitude differences with music signal?
Now in my researching this topic I came across this Audioholics article which seems quite sensible in it's approach & does as survey of the research papers on the topic
In it a chart of research results over 60 years is given & the lowest JND is 0.25dB F.E. Toole and S. Olive, "The Modification of Timbre by Resonances: Perception and Measurements", JAES vol 36, # 3, March 1988, pp 122-142
The author states "Toole and Olive, on the other hand, in their 1988 study used pink noise for their acoustic signal source and determined that a 5 kHz resonance, with Q = 1 was just detectable at .25 dB." But later "The .25 dB figure quoted from the Toole & Olive research seems to contradict this (his JND of 0.75dB or 1dB), but consider the filter Q = 1. That's a pretty broad chunk of the audible spectrum over which that resonance exists. With the ear-brain combo performing an integration across that broad a portion of the audible spectrum than its easy to see how a large amount of acoustical energy is captured, leaving a change that small noticeable. However, pink noise is not real world and one thing my research has shown is that the hearing process reacts very differently to different types of sound; a .25 dB detectable difference using real music just isn't plausible and the research supports that."
He goes on to state "In this particular article, I settled on a minimum discernable difference dB value of .75 - 1.0. My experience has shown that this is what the average listener, under average listening conditions, listening to music played back through typical consumer-grade audio gear will be able to clearly identify - and do so repeatedly."
Now loudness is a psychoacoustic phenomena i.e intensity + auditory processing -> perception of loudness so some factors relating to this. The frequency filterbank (ERBs) that we split the sound into & analyse over is instrumental in how we perceive loudness. In other words, a single tone whose frequency falls into one filterbank, will be perceived as quieter than a wider band signal that spans more than one frequency filterbank, given that both are the same intensity (dB).
A consequence of this is that we are more sensitive to broadband noise intensity than to single tones & hence there is a curve of noise sensitivity called ITU-R 468 which defines our sensitivity to noise intensity & it is different to the Fletcher-Munson curves. here's the comparison which shows that we are more sensitive to noise @ 6KHz frequency than to a single tone at this frequency by > 12dB as can be seen here:
So, my questions again
- what evidence do we have that intensity mismatches of > 0.1dB will be perceived as quality issues with music signal
- what is the JND for amplitude differences with music signal?
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