"Doppler Shift" reflected from fixed objects?

More likely to me is the effect of intensity on pitch. Louder tends to sound sharper.

Tim

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On Apr 30, 2018, Adrian Tuddenham wrote (in article):

It will take some math to tell. From your friend, get the actual dimensions and locations. Then compute the phases of the echos coming off each column and algebraically sum the echos. Compute this as a function of frequency. There will be peaks and valleys. The ear is most sensitive around 3 KHz.

The above is straight from the theory of phased-array radars, and there are many university lectures on the web about this.

Joe Gwinn

A reflection of a fixed object won't alter the frequency.

Assuming there isn't a sound system in place, the only explanation I can think of is where there where some frequencies are absorbed (for whatever reason) , those that are left provide this perception of being flat.

I doubt a singer's voice is pure, in a similar same way a chord on a piano is not pure. If one of those notes is missing or attenuated then this could exhibit the same effect.

An audience is very good at being an absorber of sound so it is not that surprising the effect is no longer apparent.

BICBW

A Doppler reflection of a pure sine wave creates new frequencies in the reflection; no fixed reflector/delay pattern can do that, in the way that an ideal FIR filter doesn't create new spectral lines. But staged reflections could sound a lot like Doppler. She has a good ear.

ns

re

Both of you are pretty far off base. Phased array radar has nothing to do with Doppler shift and it doesn't have to do with the phasing of multiple r eflections. It has to do with the fact that an object is actually moving w hen reflecting a sound, so the *only* reflection is constantly impacting th e phase of the returned signal. The analog to the multiple phased returns in a church would be an echo chamber. That's why they try hard to restrict the echos in any music hall. The want some return so it sounds "live" but too much is disturbing. None of the above will alter the actual pitch.

Rick C.

As an occasional singer, I can testify that perceived pitch is easily altered by the environment. This must be why even top-class performers often sing off-key on stage.

There's no such effect in the steady state, obviously, but I could imagine a psycho-physical effect of that sort, with the number of echoes rattling round.

Cheers

Phil Hobbs

that

I was tickled, many years ago, to learn that the unit of absorption for acoustic purposes is "square foot of open window". Maybe there is a proper metricated equivalent these days...

Mike.

the psycho acoustic effect of change in PERCEIVED pitch vs loudness is well known.

mark

There were line-source speakers on the backs of some of the columns. I noticed they were mounted exactly vertical and quite high, so the sound reaching the congregation below would be very poor because of the differing path lengths from individual drive units. However, a clear echo would come off the back wall.

There was no service in progress when I visited, so I couldn't hear how the system sounded; if it used a frequency shifter to overcome feedback, that might have accounted for the echo being lower in pitch.

Maybe different frequencies have different time of flights/ dispersion. (have you ever clapped into a long pipe?)

George H.

I'm not sure if it is normal to frequency shift up or down. Most articles don't say and can only find one which said a unit shifted 5Hz higher.

I'm very conscious that perception of pitch is complex. Shepard tone is a good an example!

Yes, and I seem to remember getting a frequency-drop effect by clapping my hands at the entrance to a redundant canal tunnel. I'll have to try that again and record it.

Several people have commented that movement is essential for creating doppler shift, but changes in the path length are the real underlying cause. Normally the change in path length could only be produced by movement of the observer, the source or the reflector, but I am wondering if the effect of a moving reflector could be created by successively reflecting from multiple stationary reflectors at progressively increasing distances.

I have only once noticed the direction of shift; that was in a really bad system, made conspicuous by its mis-operation. It shifted down - and reminded me of water going down a plug-hole.

That would be equivalent to running a signal through multiple delay lines and summing the result. That doesn't create any new frequencies.

Only if you are looking for another joke based om oriental people's inability to distinguish "l" and "r" sounds...

Mike.

Right no new frequencies, but it can change the perceived sound.

George H.

A transient standing wave effect with the null points moving around in space would produce an amplitude modulation at the listener's position and that does create new frequencies.

Culverts under highways work too. You get a sound that is chirped.. the higher frequencies have a longer path length. (Well in detail it's more complicated than that.)

George H.