You can create beats with "slightly" different frequencies. But we do definitely perceive great differences between random and deterministic components. They depend on the ‘composition’ of the contributing sinusoids. But also on the length of the period of listening. And in such compositions both the choices of frequencies and phases have strong influence.
Reference from here: ( Direct copy & paste from here: ) 1
Please calculate with high resolution the following three compositions,
using five sinusoids:
- 10,000 / 10,002 / 10,004 / 10,006 / 10,008 Hz. All sine contributions.
In that case you will hear the high tone that corresponds with 10,004 Hz but
with a strong beat of 2 Hz.
- 10,000 / 10,004 / 10,008 Hz. All three sine contributions.
10,002 / 10,006 Hz. Both cosine contributions. So a 90 degree phase shift.
In that case you will hear the high tone that corresponds again with 10,004 Hz
but now with a strong 4 Hz beat.
- 10,000 / 10,002.0333 / 10,004 / 10,006.0333 / 10,008 Hz. All sine contributions.
In that case you will hear the high tone of 10,004 Hz again,
but within a period of 30 seconds
and starting with a 2 Hz beat
after 7.5 seconds the beat will gradually change into a 4 Hz beat.
After 15 seconds the beat is back again at 2 Hz.
At 22.5 seconds again at 4 Hz
and after 30 seconds the composition ends with a 2 Hz beat in the 10,004 Hz tone.
If you change the sine contributions of 10,002.0333 and 10,006.0333 Hz into cosine
starts with a beat of 4 Hz,
2 Hz at 7.5 sec,
4 Hz at 15 sec,
2 Hz at 22.5 sec
and finally 4 Hz at 30 sec.
In all these proposed experiments the calculation of the different contributions to the sound energy frequency spectrum resulted per experiment in exact predictions of the final beat rhythm.
Reference from here: 2
Based on the concept that our hearing sense is differentiating and squaring the incoming sound pressure stimulus, this mechanism evokes in front of the basilar membrane the sound energy frequency spectrum.
So it is the sound energy signal, present inside the perilymph fluid, as a uniform
pressure stimulus all over the volume. And therefore all the existing Fourier frequency components in the sound energy signal are present inside the perilymph to stimulate the basilar membrane including their relative amplitudes and their relative, but
extremely precise, phase relations.
Direct copy & paste from here: www.a3ccm-apmas-eakoh.be/pcbwp/experiments.htm
About 10 kHz experiments (frequencies together with some prescribed phase relations
in a standard summation procedure to compose a Fourier series) with a 0.0625 Hz detuning, there exists an accuracy in the periodicity pattern of 6.25 parts per million.