SPEED, PITCH, TEMPO, KEY (From Callerlink 152 June 2002)
By: Jeff Garbutt, Western Australia

When buying turntables, minidisks or CD players we are always looking for that control to give us variable "something". And the products they sell us come with all sorts of terms like"variable speed" or "variable pitch". But, what exactly do these terms mean? Even the Hi-fi salesman doesn't really know!

From Oxford dictionary we get the following definitions

- Tempo - time, rapidity of movement; characteristic speed and rhythm of movement
- Pitch - quality of sound governed by rate of vibration of string etc
- Key - system of notes definitely related to each other based on a particular note based on a particular note and predominating in a piece of music

And from Hanhurst website:

- Speed: The playback rate of a song. Changing the speed of a track will affect both the tempo and pitch, much like adjusting the pitch on a record player would. Doubling the speed would halve the length of the track, and raise the pitch by one octave. 
- Tempo: The rate at which the beat proceeds. Changing the tempo will alter the BPM, while preserving the pitch. 
- Pitch: The key and range in which a song is played. Changing the pitch will raise or lower the tones in a song, while maintaining its original tempo. 

"Jeffspeak"

Locate the note "Middle C" on a piano, which is a note that produces a musical tone with a dominant frequency of 256 Hertz, (256 cycles per second). Just imagine you are playing the note "Middle C" on a piano at a rate of 128 beats per minute. 
- Tempo - If you vary the tempo, you will vary the rate at which the note gets played. If you adjust tempo down by 10% the tempo will change from 128 bpm to 115.2 bpm. The note itself will not change in frequency.
- Pitch - If you vary the pitch you are actually changing the dominant frequency of the note. For instance if you adjust pitch down by -10% you will adjust the frequency from 256 Hertz to 230.4 hertz - which is a note somewhere between "A sharp" and "B". The tempo (BPM) is not affected.
- Key - Is a more specific type of pitch. Changing the key works similar to pitch, but the tones of music are changed from one musical note to another musical note. Not somewhere between two musical notes. 
- Speed - Variable speed will change both the "Tempo" and "pitch". Which is what happens on variable speed turntables.

So what does it all mean ?

Ultimately, the effect that we are after is to have variable tempo. Although in some cases callers have been known to alter the speed of a record to bring it within their voice range.

Turntables will alter both tempo and pitch.

In the case of adjustable CDs and Minidisks - they actually give us "variable tempo". But most manufacturers call them "variable pitch".

True variable "key" is generally done using "key changers". The reason is that musicians want the new notes generated to correspond exactly with a real musical note. Not halfway between two notes. 

Confused ? I Hope so, because I still am ! 

 

What do I mean by "Dominant Frequency"

Musical notes are not exact sine waves set at one particular frequency. They are actually very "messy" waveforms. And we can be very thankful for that - as it is this "messiness" that makes each particular instrument so unique and wonderful.

Listening to a pure sine wave is actually quite boring.

A musical note actually contains a combination of many sine waves, all set at slightly different frequencies and different levels (or volumes). And the overall shape is not always symmetrical. But there is always one dominant frequency, which is stronger than all the others. It is the deviation of frequencies either side of the "dominant frequency" that gives each musical note an interesting character. 

And it is the variation of all this "messiness" between different instruments that makes a "piano sound like a piano" and a "guitar sound like a guitar" even though they are playing the same musical note.