The Doppler Illusion, why is it so hard to understand?
Apr 7, 2024 at 12:53 AM Thread Starter Post #1 of 39

Redcarmoose

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“Four studies illustrate a new auditory illusion associated with the Doppler effect and demonstrate a new influence of dynamic intensity change on perceived pitch. Experiment 1 confirmed the existence of a popular belief that the pitch of a moving sound source rises as the source approaches. Because there is no corresponding rise in frequency, the authors refer to the perceived pitch rise as the Doppler illusion. Experiment 2 confirmed that the effect occurs perceptually, so the belief in a "naive principle" of physics has a perceptual basis. Experiment 3 confirmed the effect does not occur under matched static conditions. Experiment 4 showed that the influence of dynamic intensity change on perceived pitch occurs outside the realm of Doppler stimuli. The findings support a dynamic dimensional interaction of pitch and loudness, with marked differences in the perception of pitch and loudness under static and dynamic conditions. (PsycInfo Database Record (c) 2024 APA, all rights reserved)”

Definition:
Doppler effect in physics is defined as the increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move towards (or away from) each other. Waves emitted by a source traveling towards an observer get compressed.

Example:
 
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Apr 7, 2024 at 4:09 AM Post #2 of 39
I’m not sure what research you’re referring to or exactly what you’re claiming. The Doppler Effect causes an increase and then decrease in pitch/frequency as well as in intensity, are you claiming it doesn’t actually change and it’s just a perceptual illusion?

G
 
Apr 7, 2024 at 4:44 AM Post #3 of 39
I’m not sure what research you’re referring to or exactly what you’re claiming. The Doppler Effect causes an increase and then decrease in pitch/frequency as well as in intensity, are you claiming it doesn’t actually change and it’s just a perceptual illusion?

G
It is more confusing though. :)


A couple ideas as to why.

1)
Study one was a survey that confirmed the existence of a popular belief that the pitch of an approaching sound source rises, even though its physical frequency at the point of observation falls. The fact that this belief has worked itself into the literature with seemingly no physical explanation for the phenomena is further evidence that the belief is widespread.


2)
Study two confirmed that subjects presented with simulated Doppler shifted stimuli actually perceive a pitch rise, so the belief was not due to an error in memory. These results demonstrate that a rise in pitch can be experienced under various conditions of falling frequency. Specifically, a Doppler shifted tone in which there is no rise in frequency can produce an illusory rise in pitch. We therefore refer to this perceived rise in pitch as the "Doppler Illusion." Wave form complexity and frequency range were found to significantly affect the magnitude of the illusion.

As the sound source approaches, perceived pitch rises while physical frequency remains constant, then falls. The rate of change in intensity may affect judgments about changes in pitch.

3)
Study three was a control condition that confirmed the pitch rise found in experiment two does not occur under matched static conditions. Subjects were presented with static tones that corresponded in frequency and intensity to the portion of the dynamic Doppler tone where the pitch rise was perceived.

Our results support dynamic change as a fundamental element in the perception of the Doppler illusion. The findings provide evidence for marked differences in the perception of pitch and loudness under static and dynamic conditions. It appears that the illusion is at least in part due to the dynamic nature of Doppler stimuli. Observers may be inaccurate in judgments of pitch change because of the complexity in the rate of change in intensity and frequency. A doppler shifted tone exhibits an accelerating rate of change in intensity, even when the velocity of the sound source remains constant. As the source draws closer to the observer, this increasing rate of change in intensity may influence real time judgments about changes in pitch (which is also changing at an increasing rate in the opposite direction).
Degree of pitch rise increases with frequency and wave form complexity.

In any event, it is clear that in the case of Doppler shifted stimuli, the relationship between pitch and loudness takes on new characteristics that have not previously been addressed. While this is important, it is likely that these types of characteristics are not limited to the dimensions of pitch and loudness, but are revealed by an appropriately dynamic means of studying dynamic dimensions. Further research that considers holistic dynamic stimuli will likely yield a more thorough and ecologically valid understanding of other perceptual dimensions.
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4) A forth, but there are more.
Historically, auditory pitch has been considered to be a function of acoustic frequency, with only a small effect being due to absolute intensity. Yet we found that when tones are Doppler shifted so that frequency drops, the pitch dramatically rises and falls, closely following the pattern of dynamic intensity change. We show that continuous intensity change can produce pitch variation comparable to a frequency change approaching an octave. This effect opposes and is an order of magnitude larger than the well-known effect of discrete intensity change in the frequency range employed. We propose that the perceptual interaction of continuous changes in pitch and loudness reflects a natural correlation between changes in frequency and intensity that is neurally encoded to facilitate the parsing and processing of meaningful acoustic patterns.
 
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Apr 7, 2024 at 5:02 AM Post #4 of 39
I’m still not clear exactly what you’re claiming. The pitch most definitely is raised when the object/vehicle approaches and then lowers when it passes, it’s not a perceptual illusion. This can be easily objectively verified by simply examining a spectrogram of a recording of a vehicle “pass-by”.

G
 
Apr 7, 2024 at 5:03 AM Post #5 of 39
I’m still not clear exactly what you’re claiming. The pitch most definitely is raised when the object/vehicle approaches and then lowers when it passes, it’s not a perceptual illusion. This can be easily objectively verified by simply examining a spectrogram of a recording of a vehicle “pass-by”.

G
1) Specifically, a Doppler shifted tone in which there is no rise in frequency can produce an illusory rise in pitch. We therefore refer to this perceived rise in pitch as the "Doppler Illusion." Wave form complexity and frequency range were found to significantly affect the magnitude of the illusion.
 
Apr 7, 2024 at 5:07 AM Post #6 of 39
If you believe the universe is expanding.

The Doppler red-shift of light observed from distant stars and galaxies gives evidence that the universe is expanding (moving away from a central point). This allows for Big Bang Theory, because after a “bang” occurs all of the matter moves away from the point of origin.
 
Apr 7, 2024 at 5:10 AM Post #7 of 39
Specifically, a Doppler shifted tone in which there is no rise in frequency can produce an illusory rise in pitch.
Sorry, I still don’t understand your point, a “Doppler shifted tone” is by definition a “rise in frequency” (when approaching) and again, it’s easily verified with a spectrogram. If there’s no rise in frequency there’s no Doppler shifted tone. Your assertion here is false.

G
 
Apr 7, 2024 at 5:12 AM Post #8 of 39
Apr 7, 2024 at 5:14 AM Post #9 of 39
I’m still not clear exactly what you’re claiming. The pitch most definitely is raised when the object/vehicle approaches and then lowers when it passes, it’s not a perceptual illusion. This can be easily objectively verified by simply examining a spectrogram of a recording of a vehicle “pass-by”.

G
The frequency is higher at the listener's position than what the source is emitting because of the movement, but it does not go up as the source moves toward the listener. And yet, many people under some conditions(depends on the sound and loudness and what not) feel like the pitch in indeed going up before passing the listener. Which has to be related to loudness, as the frequency doesn't go up and even goes slowly down.


The frequency is higher for an approaching object compared to the frequency the source is emitting, because of the speed at which they get closer, but that's it. Unless the moving source keeps accelerating, the frequency doesn't keep going up.
 
Apr 7, 2024 at 5:27 AM Post #10 of 39
The doppler effect for light is symmetrical - it doesn’t matter whether the source or the viewer is moving.

The doppler effect for sound does indeed depend on whether the source or the listener is moving…but (and this is key) whether they are moving relative to the air.
 
Apr 7, 2024 at 5:27 AM Post #11 of 39
The frequency is higher at the listener's position than what the source is emitting because of the movement, but it does not go up as the source moves toward the listener. And yet, many people under some conditions(depends on the sound and loudness and what not) feel like the pitch in indeed going up before passing the listener. Which has to be related to loudness, as the frequency doesn't go up and even goes slowly down.
Ah, got it, the claim is that the pitch appears to continue to rise as the vehicle approaches at a constant speed (not accelerating) and that continued rise is a perceptual illusion. Yes, again, a spectrogram of a vehicle pass-by confirms this, the pitch is raised but constant until just before the vehicle passes (at which point the pitch lowers) but the intensity continues to rise until the vehicle passes. This is well known/established and has been employed in practice for decades.

G
 
Apr 7, 2024 at 5:39 AM Post #12 of 39
The frequency is higher at the listener's position than what the source is emitting because of the movement, but it does not go up as the source moves toward the listener. And yet, many people under some conditions(depends on the sound and loudness and what not) feel like the pitch in indeed going up before passing the listener. Which has to be related to loudness, as the frequency doesn't go up and even goes slowly down.


The frequency is higher for an approaching object compared to the frequency the source is emitting, because of the speed at which they get closer, but that's it. Unless the moving source keeps accelerating, the frequency doesn't keep going up.
Thank-you.
 
Apr 12, 2024 at 7:45 PM Post #13 of 39
Ah, got it, the claim is that the pitch appears to continue to rise as the vehicle approaches at a constant speed (not accelerating) and that continued rise is a perceptual illusion. Yes, again, a spectrogram of a vehicle pass-by confirms this, the pitch is raised but constant until just before the vehicle passes (at which point the pitch lowers) but the intensity continues to rise until the vehicle passes. This is well known/established and has been employed in practice for decades.

G
This is fascinating, I did a little more digging and part of the reason why we do indeed perceive a changing increase/decrease in the pitch (and not just a constant increased/decreased pitch) despite the source moving at constant velocity relative to the observer is due to the change in radial velocity.
Vsource may be constant but the radial velocity (the actual velocity observer and source) changes due to the change in angle between source and observer
 

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Apr 13, 2024 at 4:06 AM Post #14 of 39
This is fascinating, I did a little more digging and part of the reason why we do indeed perceive a changing increase/decrease in the pitch (and not just a constant increased/decreased pitch) despite the source moving at constant velocity relative to the observer is due to the change in radial velocity.
That’s interesting, do you have more information or better still a source of that information? The actual pitch doesn’t change (until the passby occurs) or if it does change, it’s too small of a change to see on a spectrogram and therefore not audible. So, I’d like to know more about how the radial velocity affects perception.

G
 
Apr 13, 2024 at 4:58 AM Post #15 of 39
Pitch and frequency need to be kept clearly separated here.
 

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