Re: HRTF's

[Kevin Austin <kevin.austin@xxxxxxxxxxxx>]

I think there may be some confusion here between low frequency signals, and [low frequency] sine tones.

Few (if any) low frequency signals are sine tones.

It is my understanding that the pinna causes time delays in a signal. When I add a sine wave to a delayed sine wave, I end up with the same wave shape, a sine wave -- of different amplitude, but not of different shape.

A signal from directly in front will not sound the same as one directly from behind (or below) because of the shadow effect of the pinna (or body).

If the "low frequency signal" were to be (in an extreme example), a 25% pulse-width wave at 150 Hz, as the elevation changed, so would the waveshape. Try this with a simple DAW mixer. Generate 200 ms of the 25% pulsewave on one track. Duplicate it onto another track. Add a 5 ms delay at the start. Duplicate it onto a third track. Add a 12 ms delay at the start. Mix the three tracks together.

The frequency is 150 Hz, but it is a now a "staircase" wave, and sounds different from the 25% pulsewave. There are (as I understand it) no new high frequency components, but the two signals do not sound the same. (The phase of the higher partials has changed.) In a 'real-life' situation (in my experience), under some conditions, there can be a sense of elevation (even without real elevation of the source) based on these changes of phase.

Kevin




On 2010, Aug 30, at 11:48 AM, Ranjit Randhawa wrote:

> Dear List,
> Could some one help to clarify as to whether HRTF's would introduce high frequency components to a low frequency sinusoid (let it be 300 hz) in determining its elevation.

> Further, would this signal sound any different if it was in front at zero degree elevation and azimuth versus at some other location?

> I guess I am also trying to find out how the pinna would interact with the signal to create any high frequency components and therefore will our ability to determine elevation of low frequency signals be degraded considerably?

> Sorry for so many questions, I have not been able to find out any references (net accessible) to such day dreaming.
> Thanks for your help in advance, sincerely,
> Randhawa