I had a few hypothesis going into this:
- The larger (Bb / C) tubas would have more noise at higher pitches - Conclusion: False
- The smaller instruments would have a more pure tone at higher pitches, but there would be visible distortion at lower pitches - Conclusion: False
- The open-bugle notes would show some sort of better quality than notes with valves - Conclusion: False
- The fundamental (2nd partial) would show some sort of better quality than higher partials - Conclusion: False
- Melton Mienl Weston 2250 (F)
- Besson Soverign (Eb)
- Melton 30 (C)
- Besson Soverign (Bb)
Here's a fourier analysis of the F tuba playing its fundamental (F2):
The first thing I liked was that the partials/harmonics are clearly visible. I added a few note names at the top. In the first octave, you only get the root note. But in the next octave, you get the fifth added. In the third octave, you get the major third and dominant seventh creating a reasonable chord! After that, the we start getting to the -80dB range, so it's pretty quiet. I was really surprised to see how loud those partials were. Volume here is in dB, so a 3dB drop on this plot represents the volume being half as soft. I repeated this with a few other instruments, and they all exhibit this in some form or another.
Here are the four tubas playing a Bb in the middle of the bass clef: If I compare these instruments, there are a few things that stand out. The main one is that you can actually see each tuba's quality. The best sounding tuba here was the C tuba. Here we can see that the space between partials is very low. This means there is very little noise between each partial. It also has the quietest 2nd partial (the others are much louder). The Bb and Eb really start to show a lot of noise from the 3000-5000 Hz range, and these were definitely the worst sounding tubas of the set.
I did a few other recordings and here were some of my takeaways:
I tried to play a pedal F (F1) with the F tuba, open-bugle and then with all five valves pressed and slides pulled. With the pedal, F1 was actually one of the quietest notes played. F2, C3, F3 ... were all louder than it, up until around C5. When comparing the two plots, the C4-F4 partials were quieter when played open-bugle, while they were about the same volume as the F2-A3 peaks when played with valves pressed.
In a lot of the notes, the Eb tuba had louder harmonics. I interpreted this as sounding "brighter". It also had more noise between each harmonic and a lot of noise above 1000 Hz which I interpreted as a "windy" sound.
I didn't see any tubas looking better than the others when playing in a certain range, or playing their fundamental. That surprised me. It seems that the tuba's quality dominates the differences. There were lots of cases where high notes looked just as good on the F as on the C and cases where low notes looked just as good on the F as on the Bb. I was expecting Eb would be a note that would shine for the Eb tuba (open) and compromise the C tuba (2+3).
I tried Bb3 on a few other instruments. Trumpet surprised me in that it was louder in its partials from Bb4 to Bb6 were all louder than Bb3. That goes well with the "louder harmonics=bright" theory.
Curious if anyone else thinks this is interesting.