So now we have a simple tone A4 and also A5 its first harmonic, a musical term for the note with twice its frequency.
What happens if we play these at the same time? Before we can do this we need to know how to play them together. There are two important characteristics that we need to take account of. The scientist calls these the amplitude and the phase. Here are some pictures to illustrate this.
At the top we have an A4 sine wave. Below it we have an A5 wave, at twice the frequency. Below it we have the same A5 shifted a bit to the right. This is often called a phase shift. Below it again we have the A5 wave which is half as high. This is an amplitude change. Finally there is an A5 which is one tenth as high..
It is important to notice that in the field of sound the amplitude is measured in decibels, or dB for short. For most purposes we can think of halving the amplitude being the same as reducing it by 6dB. Strictly this means a halving of the power in the wave, rather than magnitude of the pressure variation.
Here are a few other examples. A reduction of a quarter is -
Now listen to some of these:
You should find no difference at all as a result of a simple phase shift. You will have a good feeling for the difference in loudness that 6dB and 20dB make. You can experiment to see what a drop of 40dB makes. I can hear it, but is scarcely shows up on the plot. I am not sure if the software is doing some compensation for the fact that it is very quiet..
