Tuning pure unisons is so important we can't leave it up to ETDs or opinion.

The International Piano Technicians School has develop a way that not only objectively measures the quality of a unison using specific criteria that make sense, the method allows students to hear exactly what a good unison sounds like and exactly where their unisons can be improved.

Procedure for Testing and Marking Unisons

1) Tune your unisons.
2) Use Oceanaudio to filter out the first four partials.
3) Use the following marking rubric to score each partial.
4) Add up the four partial marks and divide by 16. A passing mark is 80%. For concert work, you need a 90%+.

Marking Rubric for Partials
1) Each partial is marked out of 4
2) Analyze the first 2 seconds of each filtered partial.
3) Ignore the first +/-0.2 seconds. Any blips in the attack are ingnored.
4) Goal: The volume must decay smoothly. If it increases within the sustain from +/-0.2s to 2s, it looses marks.
5) If the volume doubles, it looses 1 mark each time.
6) If the volume increases but by less than double, it loses 1/2 mark each time.
7) The "Boo Waa" exception.
If the volume decreases early, around 0.5 seconds and then increases and continues to decrease smoothly, no marks are lost.

NOTE: On rare occasions a unison will pass but the technician doesn't like its sound. In those cases, often filtering the 5th and 6th partial will uncover the problem.

Partials to Filter
The first four partials are appropriate to mark for notes C4-B4. However, as we move up the keyboard, the partial frequencies become too high to hear and their volume diminishes. Also, as we move down the keyboard, the higher partials that we didn't hear before, become audible.

For this reason, the four partials we will measure will change depending on which octvae is the note. 

Refer to the table below. (Mark the total partial score out of 4 x number of partials. E.g. if marking C6, add the partial scores of partials 1 and 2 and mark out of 4 x 2 = 8.)

Unison Marking Example

The image below is of one student's unison. Each partial was filtered.
P = Peak, which means a volume increase that doubles. (loses 1 mark)
H = Half Peak, which means a volume increase that increases wbut less than double. (Loses 1/2 mark)
X = insignificant peak, which loses 0 marks.
Volume increaszes that are less than 25% are ignored.