I was walking down the street with my earphones in, nothing playing, and I noticed a car alarm blaring from behind me. I took my earphones out, and the car alarm shifted slightly in frequency!

I repeated this a few times, putting in and taking out the earphones, and must have looked absolutely insane to anyone watching at the time, but I found that the earphones being in my ears, nothing playing, repeatably and consistently caused a slight pitch shift in the car alarm. I didn't change speed or direction as I was carrying out this experiment, so it wasn't simple Doppler shift, and I changed the amount of time the earphones were in and out of my ear to be sure it wasn't some effect in the alarm itself that I happened to phase-align with.

What explains this pitch shift?

  • 1
    $\begingroup$ Did you try covering your ears in other ways? $\endgroup$
    – user234190
    Jul 5, 2019 at 23:46

1 Answer 1


This is a well-known effect in psychoacoustics: your earbuds muffled the sound, and the pitch of a sound varies with its intensity. Generally, low frequencies sound lower in pitch when louder, while high frequencies sound higher in pitch, with the turnaround region about 3 kHz. You can play with an example here.

Unfortunately, it's not a pure physics phenomenon, but a rather more complicated biological thing. Furthermore, even though this effect has been documented for almost a century, there doesn't seem to be any agreement today over why it happens. From the psychoacoustics textbook An Introduction to the Psychology of Hearing:

It has sometimes been argued that pitch shifts with level are inconsistent with the temporal theory of pitch; neural inter-spike intervals (ISls) are hardly affected by changes in sound level over a wide range. However, changes in pitch with level could be explained by the place theory, if shifts in level were accompanied by shifts in the position of maximum excitation on the BM. On closer examination, these arguments turn out to be rather weak. Although the temporal theory is based on the assumption that pitch depends on the temporal pattern of nerve spikes, it is also assumed that the temporal information is "decoded" at some level in the auditory system. In other words, the time intervals between neural spikes are measured and transformed into another representation. It is quite possible that the mechanism that does this is affected by which neurons are active and by the spike rates in those neurons; these in turn depend on sound level.

The argument favoring the place mechanism is also weak. The results of physiological experiments using animals and forward-masking experiments using human subjects (see Chapter 3, Section 9) suggest that the peak in the excitation pattern evoked by medium- and high-frequency tones shifts towards the base of the cochlea with increasing sound level (Moore et al. , 2002). The base is tuned to higher frequencies, so the basal-ward shift should correspond to hearing an increase in pitch. At high sound levels, the basalward shift corresponds to a shift in frequency of one-half octave or more. Thus, the place theory predicts that the pitch of a medium- or high-frequency tone should increase with increasing sound level, and the shift should correspond to half an octave or more at high sound levels. In fact, the shift in pitch is always much less than half an octave. Another problem for an explanation in terms of place theory comes from the observation of Thurlow (1943) that the pitch of a tone presented to one ear can be changed by presenting a tone of the same frequency to the other ear, provided that both tones are of fairly high intensity. The change in pitch is in the same direction as that produced by a physical increase in intensity. The pitch shift may have more to do with the loudness of the tone (which depends on information from both ears) than with the intensity in each ear (which determines the position of the peak excitation on the BM).

In plainer English, nobody knows whether this effect is due to a difference in how the neural impulses get processed in the brain (the temporal theory), or how the cochlea is excited in the ear (the place theory). It doesn't seem to fit well with either one of these two theories of pitch. The book concludes:

At present, there is no generally accepted explanation for the shifts in pitch with level.

One of the great things about everyday physics is that, using only your own senses, you can go so quickly beyond our knowledge!

  • $\begingroup$ A possible alternative explanation is that the earbuds are causing some mechanical stress within the ear. For example, I once noticed that the apparent pitch of sounds increases (the apparent frequency changes by 20% or 25%) simply by clamping my jaws together by biting hard on something. The pitch change is roughly proportional to the biting pressure. $\endgroup$
    – alephzero
    Jul 6, 2019 at 2:19
  • $\begingroup$ @alephzero, that effect occurs because the acoustic nerve suffers crosstalk with the nerves controlling the jaw muscles, which share a common conduit through the skull. I have tinnitus, and can modulate the intensity and pitch of it by clenching my jaw. $\endgroup$ Jul 6, 2019 at 4:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.