Hello Andrew,
Quote:
macrae11 wrote:
 According my understanding of your hypothesis of “gate time” there would be a noticeable delay of lower frequencies from higher frequencies. I'm just guess here, but if you're saying that there's a 50ms “gate time” at 40Hz, than it might be logical to assume that there is a 100ms gate time at 20Hz, and a 25ms gate time at 80Hz? |
Your understanding of that is incorrect, and attempting to extrapolate that to a simple frequency dependence magnifies the misunderstanding. Perception of sound is not an instantaneous process, it is affected by what is presented to the ear over a period. A demonstration of that is Temporal Masking, in which a loud sound can prevent us perceiving sounds that arrive up to 100ms after it (not surprising) but also sounds that arrived up to 20ms
before it. That does not mean that we simply delay everything to see what might come next, but that our perception of what arrives is affected by all the arrivals within a time window. There is no perceived delay.
Quote:
| macrae11 wrote:
In regards to the first part of your post, you claim that humans need to hear an entire cycle, or at least a half cycle of a waveform in order to identify it. To my understanding I don't believe this is true. I tried to find some research to this effect, but haven't found what I was looking for as of yet. |
Think about the spectrum of a short segment of a tone. How much of the tone do you think would be needed before the fundamental can be seen on a plot of the tone's spectrum? The inner ear acts somewhat like a spectrum analyser, with different parts of the spiral portion sensitive to different frequencies. Until enough of a tone has arrived at the ear there is no content at the fundamental to be detected, just some spectral content related to the evolving envelope of the sound. As if that was not problem enough, people seem divided between those who even perceive fundamentals at all and those who rely almost entirely on overtones (google "missing fundamentals") but in any case sufficient signal needs to be received to establish the spectral content for the auditory system's pattern matching to work on.
Meanwhile to return to the original question
as to whether applying a filter to the direct sound at a low frequency means what we hear sounds correct or not, let's consider a very simple case of a 40Hz tone arriving at the ear accompanied by a single reflection from a wall a few feet away. For convenience let's have a path difference that corresponds to a quarter wave, 6.25ms, and allow the reflection to be as large as the direct signal. The signals arriving at the ear are then the direct sound from the speaker and a quarter wavelength delayed version. The sum of these two, using basic trig identities for sums of sines, is a sine wave at the original frequency with a 1/8th wavelength phase shift and an amplitude of sqrt(2) times the original, so as far as the listener is concerned the tone has been made louder. To get the tone to the level it would have had without the effect of the reflection we need to reduce the level of the original sound by 1/sqrt(2). In doing that the 1/8th wavelength phase shift remains, but the level is corrected and the listener is none the wiser.
In the more general case of an enclosed space there are only specific frequencies, the modal resonances, at which the multiple reflections from the room's surfaces generate a stable standing wave. The effect at those frequencies is to alter the perceived level of those tones according to the amplitude of the standing wave at a given location in the room. Altering the level of the original sound correspondingly gets us back to the level a tone would have had without the room's influence, with the proviso that nothing can be done for locations where the amplitude of the standing wave is zero and more generally it is inadvisable to boost the signal in locations where the standing wave amplitude is lower than the original signal.