[gregorio]

Pitch and frequency need to be kept clearly separated here.

Why?

G

 

[castleofargh]

Some car passes by(let's say straight line and constant speed). As it approaches the guy on the side of the road, the frequencies measured at the guy's ear are stable until they start going down(to reach the same frequencies as the ones actually emitted by the car while passing the guy, and then to get below that while the car goes away. Objective Doppler effect).
The pitch(subjective perception) can seem to progressively go up as the car gets close. That's what the guy in the paper called illusion, because the frequencies don't go up, but we kind of feel like they do(pitch).

 

[gregorio]

The pitch(subjective perception) can seem to progressively go up as the car gets close.

Ah right, I see. I was thinking in terms of musical note pitch rather its meaning of a subjective perception.

G

 

[71 dB]

Surprisingly interesting thread! I have never thought about how I perceive the pitch of sound sources moving compared to me. Indeed the pitch of a bypassing sound source should slowly drop instead of a massive fast drop at the moment the sound source bypasses the listener and starts to move away from the listener. I need to start paying attention to how I perceive Doppler effect. I admit I never thought that there would be an perceptual illusion involved.

 

[bigshot]

If it’s perceptual, why can the Doppler effect be recorded?

 

[Ryokan]

 

[71 dB]

If it’s perceptual, why can the Doppler effect be recorded?

It is a combination of physical and perceptual phenomena. Physical phenomena can of course be recorded. Stereo sound is also perceptual, an illusion even, but we still can make stereo recordings. The physical and perceptual sides are linked in more of less complex manner. To put it more precisely: We can record Doppler effect, but not Doppler illusion. The recording doesn't have the rising pitch in it, but that's what we perceive as an illusion according to this study.

I have never paid much attention to how my perception (illusion) of Doppler effect relates to the physical Doppler effect. Doppler effect just happens in everyday life and seems to have near zero consequences to anything. Pitch changes. So what? Nevertheless it is interesting to understand there is an illusion involved. Who knows, maybe this can even be used in music production to create certain sonic illusions?

 

[bigshot]

Ok. I knew there had to be a physical aspect. I have demonstration records of steam locomotives that are vivid examples.

 

[71 dB]

Ok. I knew there had to be a physical aspect. I have demonstration records of steam locomotives that are vivid examples.

Yes. That's why this is tricky. There is a real physical frequency change, but it isn't exactly what we perceive:

A sound source bypasses an observer:

Physical recorded/observed frequency: Is higher than the source frequency in the beginning and drops slowly until the sound source bypasses (minimal distance) and the frequency drops fast below the source frequency and then slower as the source moves away.

Perceived pitch: Rises until bypass and then goes down (see Fig. 2 the graph in the study linked).

 

[castleofargh]

The Doppler effect is strictly the objective phenomenon. Wavelength shifting due to relative motion. There is no mystery, not unmeasured part and no need for a human at all.

The paper that Red quoted is not about the Doppler effect itself, but about a strange way we might perceive the pitch increasing as a sound source comes closer to us. And the paper calls that "Doppler illusion" because the frequency does not keep increasing as the sound source gets closer. We somehow mistake the increase in loudness for an increase in pitch, or something like that.

 

[bigshot]

I don’t seem to be subject to the illusion. I don’t hear a change in pitch on approach, just volume.

 

[gregorio]

Is higher than the source frequency in the beginning and drops slowly until the sound source bypasses (minimal distance) and the frequency drops fast below the source frequency and then slower as the source moves away.

It doesn’t slowly drop, it stays constant (assuming a constant speed) and then drops quite quickly as it passes and then stays constant again. The pitch change actually occurs over a period typically of 0.5 - 1 second, although obviously depends on the speed of the vehicle.

Who knows, maybe this can even be used in music production to create certain sonic illusions?

It is sometimes but it’s quite rare in music production. It’s very common in film sound though, obviously there are often vehicle passbys, including aircraft. If fact there are entire sound libraries of passby but sometimes we need to create our own for various things, from artillery and other weapons or projectiles to flying insects. There are a number of plugins to help with the process and all sound designers/mixers have at least one in their collection.

I don’t seem to be subject to the illusion. I don’t hear a change in pitch on approach, just volume.

It varies, not only from person to person but for the same person, on one occasion they maybe subject to the illusion and on another occasion they may not be.

Interestingly, the effect can feel more visceral if one is subject to the illusion. So it’s quite common in sound design, when the effect needs to have particular dramatic impact, to physically create the illusion, IE. To create an actual gradual increase in freq as the vehicle/object approaches, although only a relatively small increase (typically around a semi-tone or less) compared to the size of the decrease as it passes.

G

 

[Ryokan]

 

[Whazzzup]

Next up motion parallax, lol

 

[VNandor]

With a bit of a stretch, digital FM synthesis is based on the same principle as the physical doppler effect. This is because both the doppler effect and digital FM creates changes in frequency by modulating the phase of the source oscillator. If you think about it, phase modulating the carrier by a saw wave is analogous to a car approaching someone with a constant speed. The analogy falls apart when the cycle of the saw resets because the equivalent would be the car (almost) instantaneously teleporting back from where it was approaching every time the cycle is complete.