Octave up is double the frequency.

Of course, then two octaves up would be 2X the frequency, etc.

To go downward one octave from any freq. it would be halving the frequency.

Does not matter what the original frequency really is, whether it is the Tempered Scale, whether or not it is referenced to A-440, or if it is just a lone sine wave at a frequency that is not a standard musical note, the same division applies. An example of that would be audio filter design, in which one of the specifications would be the frequency rolloff of the filter, listed in decibels/octave. For example, most audio engineers agree that the 6db/octave filter rolloff is the most "musical" sounding approach. etc.

This applies to more than just the audio spectrum also, in days gone by now it was even used to describe radio frequencies and still today in some physics it is good to use the octave designation sometimes to indicate the frequency divisions of harmonics and the like.


--Mac