Pitch is defined as the property of a musical tone determined by its frequency and intensity [1]. In most cases the tone and frequency are directly related. The higher the tone, the higher the frequency. This relationship is commonly known and understood but what is not obvious is that sounds heard by the human ear appear to increase and decrease in pitch as the intensity of the sound is varied. This is because of the non-linearity of the basilar membrane. The basilar membrane is part of the cochlea, a spiral, cylindrical tube found within the inner ear. As a tone gets louder the ear percieves its pitch to decrease as much as 10%. An experiment by Fletcher reported an interesting illustration of this effect. At normal levels, tones of 168 and 318 Hz played simultaneously created a discordant sound. These same two tones played back at a much higher volume level, however, were percieved to be in the 150 and 300 Hz octave relationship, a pleasant sound [2]. I only mention this aspect of pitch because a Sound Designer should always consider the larger psycho-acoustic effects that could be generated when manipulating and altering sound.

Pitch transposing or pitch shifting, as it's sometimes called, is when the pitch of a sound is raised or lowered from its original value. For a novice sound designer, this is probably the first major effect besides reverb to be experimented with. Although I was very young, the first time I noticed the effects of pitch shifting was when I played a vinyl record at the wrong speed. Without realizing it, I immediately understood the relationship between the change of pitch and the change of time. It wasn't long before I could hear and recognize pitch effects on television, radio and at the movies. I knew what those sound guys did to the sound I just didn't know how they made it work with all the other unaltered sounds... and so began my journey in sound design!

After collecting or creating good samples, which is a whole other topic, it's time to change sounds to suit your purpose. Luckily, much of sound design can now be done with the aid of a computer. It's a shame that all the tricks learned on tape recorders aren't needed as much anymore, I think of it as a sort of lost art form. But what drives most sound designers to do what they do isn't the mechanical act involved, only the results.

Here's a common use of pitch transposing. Notice how a single gunshot can change from a pop/crack to a ka-boom, or like a pistol into a cannon, just by lowering the pitch.

A common effect in music is called an octave divider/doubler. A musical pitch is changed to a fraction of the original and then recombined. This fraction can be an octave, a major fifth or fourth, or anything in your imagination. This effect is not limited to just music and can be used on any sound and combined in any varying amount to achieve all sorts of textures and new tones. Here's an example:

Sometimes a sound designer doesn't really want to alter pitch but instead wants to alter time. This used to be done by pitch shifting the sound and altering tape speed. Now, you just tell the computer based audio editor how long the program is supposed to be and to keep the pitch normal. You can't make huge time changes without some sort of sonic degregation but small ones are easy. Listen to the spoken fine print talk at the end of some commercials. The narrator spoke at a quick pace then the audio guy sped him up even more.

Here's a something to remember - when you change the pitch of a person or sound effect you also alter the environment that it was recorded in. Here's a soft drink can being crushed in a small recording booth. Then the same can several octaves down. That small can and small room turned into what sounds like a 55 gallon steel drum being crushed in a school gymnasium. Remember the gunshot turned into a cannon? Listen again and compare the reverb trails in each of the recordings. When you change pitch you're also changing time. When you alter time you also alter space.

From here we could go on to compare the relationships between time and pitch using modulation techniques like flanging. Bring in the subjects of equalization, comb filtering and regeneration and we'd be deep into Phase Shifting & Ring Modulation. Add to that proper envelope generation and you're going to have some interesting sounds. For now I'll leave that up to you to explore on your own. Come back soon and you're sure to find something added to this page. Until then.....

[1] Tremaine, Howard M. - Audio Cyclodpedia, 1978 Howard W. Sams p14

[2] Everest, F.Alton - The Master Handbook of Acoustics, 1981 Tab Books p44

Send correspondence to studio@newenglandsoundscape.com.

January 15, 2003