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Posts Tagged ‘software audio synthesis’

Sonatina

The above is a visual representation of the opening measures of Muzio Clementi’s sonatina, Op 26, No1 as rendered by sf2sound — a kind of command line synthesizer that takes a stream of solfa symbols as input. This is homework for an eventual ear-training program. In any case, here is the audio file:

theme

One of the challenges has been in shaping the waveforms of the individual notes so that they fit together without making annoying pops. A simple exponential decay did not work, although that is good for making the sound more or less percussive. What I discovered is that (at a minimum), one has to shape the attack and release of the note. For the moment I have done this by shaping the wave form with a simple quadratic function.

I’ve been experimenting with various settings and algorithms in order to get a better or more interesting sound. The sound file you hear is slightly more complex than the other ones I have posted. In previous version the sound was either (1) an exponentially damped sine wave, or (2) the former with some kind of shaping of the amplitude profile as mentioned above. In the current version, higher harmonics are mixed with the fundamental tone. Here is the code snippet of quad2samp where the mixing occurs:

// Form the sine wave and add harmonics to it
samp = sin(W*phase);
samp += -0.4*sin(2*W*phase);
samp += +0.2*sin(3*W*phase);
samp += -0.1*sin(4*W*phase);

I’ve observed an odd but likely well-known phenomenon (or is it an illusion?). When the sound consists of a shaped sine wave, i.e. no (deliberate) harmonic mixture, I find it painful to listen to it, even at relatively low volumes. Painful in the most elementary sense of the word, not because the poor artistry of sf2sound! When I mix in higher harmonics in some degree, the (physical) pain diminishes. I suspect this because the acoustic energy in the first instance is concentrated near a single frequency, so a small number of hair cells in the inner ear are overstimulated. When the same energy is spread among the various harmonics, albeit in unequal proportions, it is also spread over more hair cells, so that individual cells are not overstimulated. Perhaps someone who really knows what is going on can comment.

I’ll close with one more image — a close-up shot that shows how the wave forms from two adjacent notes join smoothly. The jaggedness of the sound wave reflects the addition of higher harmonics to the sine wave representing the fundamental tone.

HH

Sonatina: close-up

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