Unison Drift

“When you tune a string and add other strings and tune a unison, the pitch changes.”

This is a comment that is shared by some experienced technicians and refuted by the vast majority of other technicians.

Virgil Smith wrote about this in “Techniques for Superior Aural Tuning”

Professor Gabriel Weinreich wrote about it in “The Coupled Motion of Piano Strings”

Yet many technicians still say, vehemently, that it doesn’t exist. In fact, I have measured this effect and have found:

• A string’s pitch change by as much as 1.5 cents due to being tuned to another string in unison.

• An interval’s beat speed change by as much as 13.7%, a drastic change in progressive beat speeds if we are trying to tune beat speeds of 5.9% for Equal Temperament.

So, there is no doubt in my mind that this occurs and is significant. In my opinion, the only possible valid, logical, and scientific responses a tuner can have to this information are:

1. “I will have to judge the final trichord before moving on if I want to be efficient and not have to retune drifted intervals” or,

2. “I do not need, wish, or care to tune to that accuracy”

A response of “This doesn’t exist” or “You are a liar”, is not appropriate considering the research that gone into this.

Here is a video showing intervals changing beat speed simply by adding and removing a mute. But of course, I could have altered the video and recordings. I encourage you to do the same experiments. But take a few samples. I have found that about 10% – 20% of the notes experience unison drift when tuned to other strings.