Determining the perceived hum-tone frequency
Determining the perceived hum-tone frequency is relatively easy. Having determined your perceived hum-tone frequency you are now able to compare this frequency to measured hum-tones within your local environment. It can be checked wether the perceived humming sound can be recorded using the Spectroid-app.
We generate sine tones for comparison using a tone generator, the freely available and easy to use online tone generator Szynalski is a tried and tested tool:
Further necessary equipment
An appropriate playback device (tablet, smartphone, PC or stereo system) and high-quality headphones are required. Closed headphones are the best choice in order to reduce any background noise (e.g. humming sounds).
Our own evaluations have shown that bluetooth headphones are not the best option for determining the hum-tone frequency, since these often have a disturbing inherent noise.
If the tablet or smartphone does not have sufficient amplification for passive closed headphones, the sine signal of the online tone generator could be reproduced by a stereo system on the connected headphones for the purpose of sufficient amplification.
It is advisable to use a quiet place for the determination of the hum-tone frequency, which is as free from background noise as possible.
Steps and Sequencing
If your devices are connected correctly we can start with the test.
Since the majority of the „hum-tone-hearers“ perceive a tone in the frequency range between 30 and 80 Hz, we start with a 30 Hz frequency. The frequency is set using the slider. Next, you need to adjust the volume of the playback at a low level, so that you are just able to hear the 30 Hz sine tone. In our experience, it has been proven useful to choose a volume that corresponds approximately to the volume of your perceived hum-tone.
Now you increase the reproduced frequency of the online tone generator in 1 Hz steps using the arrow keys next to the frequency display of the online tone generator (the slide switch could also be used, however, a better adjustment is possible using the arrow-keys). Once you have reached your perceived hum-tone frequency by increasing the frequency in the tone-generator, you might experience an effect that is known as an acoustic beat.
The perceived hum-tone overlaps with the generated tone of the tone-generator until you hear a single tone that changes in volume periodically. This change is perceived as a kind of billowing. As you approach the exact hum-tone frequency, the billowing slows down until the acoustic beat completely disappears. The same effect is used by musicians to tune their instruments.
With this acoustic beat effect you should now have been able to determine your own hum-tone frequency with relative accuracy. It is recommended to repeat this experiment several times on different days in order to ensure greatest accuracy regarding the determined hum-tone frequency. If no acoustic beat effect was achieved, it could have been due to the fact that the playback volume of the tone-generator was set too high or too low. Several attempts are often necessary to achieve an acoustic beat effect.
Anyone who has been able to create an acoustic beat and / or for whom the generated sound has triggered their own hum-tone should consider the possibility that their perceived hum-tone might be a low-pitched tinnitus.
Find here a sound example for binaural beats:
The two sine signals (78 Hz on the left and 80 Hz on the right ear) generate a new pulsating tone in the brain that does not actually exist. However, this „new sound“ does not in fact arise from overlaying the different sound waves, but according to research is most likely generated in the brain stem (nucleus olivaris superior). This newly generated sound is created as an effect (binaural beats) and sounds very similar to a generated acoustic beat which you might perceive while determining the hum-tone frequency. It is therefore well suited as a sound example.
Note: playing of very low frequencies (below 30 Hz):
Very low and very high tones are perceived at a much lower volume (Link: Hörfläche / auditory sensation area), so people tend to increase the volume excessively when playing low frequencies. It is important to note that the low tones which are then heard can be severely distorted due to an overloading of the playback membrane. Therefore, people often do not hear the low frequencies that are generated by the tone-generator, but rather the distortions caused by overload. Even if it may seem as though frequencies below 20 HZ can be clearly heard, it may well be the case that the audible distortions are leading you astray. In addition, it should be noted that the reproduction of frequencies below 20 Hz is subject to severe restrictions due to the design of many headphones.