The Fourier Uncertainty Principle: Not So [Un]Certain?
The time-frequency uncertainty principle states that the product of the temporal and frequency extents of a signal cannot be smaller than 1/(4π). We study human ability to simultaneously judge the frequency and the timing of a sound. Our subjects often exceeded the uncertainty limit, sometimes by more than tenfold, mostly through remarkable timing acuity. Our results establish a lower bound for the nonlinearity and complexity of the algorithms employed by our brains in parsing transient sounds, rule out simple “linear filter” models of early auditory processing, and highlight timing acuity as a central feature in auditory object processing.In other words, the scientific foundations of lossy codes including MP3s which are based on psycho-acoustic models may in fact be based on incorrect assumptions about our perception.
In many applications such as speech recognition or audio compression (e.g., MP3), the first computational stage consists of generating from the source sound sonogram snippets, which become the input to latter stages. Our data suggest this is not a faithful description of early steps in auditory transduction and processing, which appear to preserve much more accurate information about the timing and phase of sound components than about their intensity.The test subjects for this research included non-musicians, musicians, composers and conductors and the test results found that these different groups had differing hearing acuity (i.e. some had more Golden Ears than others):
It is important to stress where the difficulty of the task lies. Our preliminary testing included nonmusicians, who where often close in performance to musicians on tasks 1 and 2 (separate time and frequency acuity), but then found tasks 3 and 4 hard (3 is frequency only but with the flanking high note as a distractor, and task 4 is timing only, with the leading note as a distractor), while musicians, trained to play in ensembles, found them easy.I first learned about this paper from an article in Ars Technica by Chris Lee. Mr. Lee concludes:
We further found that composers and conductors achieved the best results in task 5 (subjects are asked to discriminate simultaneously whether the test note is higher or lower in frequency than the leading note, and whether the test note appears before or after the flanking high note), consistently beating the uncertainty principle by factors of 2 or more, whereas performers were more likely to beat it only by a few percentage points.
The obvious conclusion, of course, is that humans don't perceive sound linearly. To a large extent, this was already known. We know volume is perceived nonlinearly, but we didn't really know much about temporal/frequency perceptions. Researchers suspected that this was nonlinear—because the brain is anything but linear—but they didn't know which model would accurately represent what goes on in the brain. Researchers and sound engineers have continued to work with linear models because they don't really know what else to use.Mr. Lee closes with this jab, "I don't have a lot of time for audiophiles with gold-coated connectors and 'unidirectional' coaxial cable, but this data is something I could buy into." But these findings can also point to why different people, especially audiophiles who spend a lot of time and energy just listening, may respond to the same hi-fi gear differently since some people are more in tune with frequency, others more in tune with time/timing, and others still perceive both better than most and different hi-fi gear excels more and less in reproducing these same values. It also helps explain why for some people MP3s are good enough while for others they aren't.