The Full Story
To understand why different types of tunings are necessary, consider stability. A more drastic change in pitch (and tension) is less stable and will needs more adjustments to stabilize. My tuning services are divided into three categories: standard tuning, pitch raise tuning, and double pitch raise tuning.
To analyze the minutia changes in tension, piano technicians divide each half step (of equal temperament tuning) into 100 cents. Knowing how many cents sharp or flat a given pitch is, we can predict how stable a tuning will be.
A standard tuning is sufficient when the overall pitch has deviated less than 10 cents. My standard tuning method involves tuning the entire piano twice. This is done for stability – to ensure the piano stays in tune for as long as possible.
Pitch Raise Tuning
A pitch raise, or pitch adjustment tuning, is what’s needed when the overall pitch is less than a half step but more than 10 cents (10% of a half step) from standard pitch. It entails tuning the entire piano three times in a row. This can be needed for pianos that haven’t been tuned in 2+ years.
Double Pitch Raise Tuning
A piano that is close to a full half step off (100 cents or more) needs a double pitch raise tuning to bring it back to standard pitch. Multiple tuning passes are needed to account for the great change in tension. This means tuning the entire piano four times in a row. This is common for pianos that haven’t been tuned in 10+ years.