NB. People using Midi instruments do not always stick to those definitions. The following if from Wikipedia
Notation that appears to be scientific pitch notation may be based on on an alternative
octave numbering. While they are still note-
For example, some MIDI documentation uses C3 to represent middle C; other writers have used C5.[ This is because the MIDI standard only defined pitches in terms of numbers (e.g. middle C is note 60), and does not specify any particular octave numbering.
The “simplest” sound is a pure sine wave, with a fixed frequency. . Here is the shape of one cycle:as plotted by a mathematical program Mathematica, which gives fine control and numbers.
And this is what a sequence of waves looks like, as viewed by Audacity, a program
which specialises in manipulating sound tracks:
And this is what a frequency of 440 cycles a second is sounds like:
If we double the frequency to 880 cycles a second then we hear a sound which is an octave higher
For the musician a frequency of 440 cycles a second is a note A. Scientists like things precise and call this note A4. Musicians call it the A above Middle C.
The note of 880 cycles per second, or for short 880Hz, is called A5; the note with twice that frequency is A6 and so on. The symbol Hz is short for Hertz, the name of a man you can read more about here:
We thus have A0:27.5Hz, A1: 55Hz, A2: 110Hz , A3:220Hz, A4: 440Hz, A5:880Hz, A6: 1760Hz,
A7: 3520Hz , A8 7040Hz, A9 14080Hz, and A10 28160Hz. This top frequency is too high for most human ears to hear at all. A1 is about the frequency of the alternating current in the elecrtic mains in the UK and can be heard at times as a low hum . A0 is hearable but not really musical .
