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Recently, someone asked me about 8:4 windows.

I have added a sound file below that is a recording of me using the 8:4 window to tune D#3 on a Steinway grand. This was taken from an actual tuning. I.e. I tuned the whole piano this way and wasn’t doing anything special just for the recording.

Basically, the check note for an 8:4 octave is the note a m6 above the bottom note, and a M3 below the top note of an octave.

For D#3, the check note is B3. (m6 above D#3, M3 below D#4)

For the D#3D#4, it is most definitely a narrow 8:4. That means for a narrow 8:4, the test will confirm m6 > (beats faster than) M3. In our case, D#3B3 > B3D#4.

The 8:4 window, which produces a pure triple octave, (D#3D#6 in our case) is:

M3 <= (beats the same, for a pure 4:2, or slightly slower than, for a median 4:2/6:3) M10 < M17 = m6 below. Specifically, B3D#4 <= B3D#5 < B3D#6 = D#3B3 The tests confirm the following: M3 <= M10 confirms a pure 4:2 or median 4:2/6:3, your choice according to the scaling of the piano. M10 < M17 confirms a wide 2:1. M3 = m6 below confirms a pure 22nd (Triple octave) The real power of this test, and what you will hear in the recording, is that, in the process of confirming the fitting of all those intervals, it is possible to hear where some of the inner intervals (M3, M10) don't fit because one note has drifted, or wasn't set properly to begin with. Using Double String Unison (an open unison technique), I am able to shim those notes until their beat speeds fit within the window, and when that happens, all the larger SBI will be virtually beatless. Listen at the end when I play all the octaves (D#3D#4, D#4D#5, D#5D#6) all the double octaves (D#3D#5, D#4D#6) the triple octave (D#3D#6) and all the D#'s together (D#3D#4D#5D#6). It's uncanny because sometimes I can't tell which octave interval I am playing when they are tuned well; each note seems to belong to the harmonic series of the other(s). Here is the recording. You will hear me adjusting many of the notes within the window, not just the D#3. [audio mp3="https://howtotunepianos.com/wp-content/uploads/2015/01/Steinway-grand-200192-D3-DSU-pure-22nd.mp3"][/audio] 0:00 Cleaning up E3 0:20 Cleaning up D#6 DSU 0:49 Raising D#3 1:10 Cleaning up D#5 DSU 1:30 Lowering D#3 1:43 Lowering D#3 2:10 Lowering D#3 2:40 Playing, in order: D#3D#4, D#4D#5, D#5D#6, D#3D#5, D#4D#6, D#3D#6, D#3D#4D#5D#6.

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