How old is the instrument?
A440 was only adopted in 1939 and although older instruments can play in tune to an ensemble tuned to A440, or in actual practice in most high schools, Bb, 233 hz, the fact is that they can sound "pitchy".
Correcting this is a bit more complicated than just tuning the instrument with the lead pipe. You have to have ears ...
Last reply was from 2015, now we live in 2021, so i don't know if anybody will read this or is it just a message in a bottle drifting on the www.
Anyways, problems might be caused by the thickness of the strings and being too thick for the nut groove. The string will not set to the bottom of the groove but slightly higher, with increased action.
So first ...
The bajo sexto strings are tuned in pairs, one octave lower than a typical 12-string guitar:1
E1-E2 A1-A2 D2-D3 G2-G2 C3-C3 F3-F3 2
This post is distilled from the Wikipedia page on Bajo sexto tuning.
1 For help ...
How does this look?
The visualization shown is plotting two signals against each other. When you hear three tones, that just means one of the two signals is actually two of the tones combined.
The form is:
f(x) = sin(ax+i) + sin(bx+j)
g(x) = sin(cx+k) + sin(dx+l)
plot (g(t),f(t)) on 0<t<2π
a,b control the frequency of tones in signal 1.
c,d control ...
Not all instruments are at the same pitch. I heard a piano tuner interviewed, who tuned pianos for the big concert halls, and he said for piano concertos he tuned the piano 1.5 cents sharp. Certain instruments are tuned slightly sharp, I think the accordion is for ensembles. Also 440 is not universal, in Vienna I believe it is 442-444.
If the marimba or ...
Although lots of bands choose A=440Hz as their tuning base, it doesn't have to be.
Marimbas are not possible to tune up/down, so they are what they are. However - all other instruments (discounting pianos/organs/Fender Rhodes et al) can be adjusted. Decades ago, in bands, where there was a piano at the venue that was enough in tune to be playable, my band ...