The spectral analyser |
What is an audio spectrum? [Professional] [Composition Pro] Sound is just a vibration of the air or of the matter in which
it propagates (water, wall,...). This vibration starts for
instance in a music instrument when the player makes his
instrument vibrate, by picking up a string, hitting a drum,...
This vibration is then transmitted to the air around the
instrument and it comes to the auditor's ear and gets registered
as a sound impression to him. So, to represent a sound signal, you need to measure the air
pressure at specific regular intervals and memorize these values.
This is what is done when you register a concert with a
microphone and a digital recorder. By playing this sequence back
into a loudspeaker, you can reproduce the exact sound that was
recorded. Because of the frequency band to which the ear is
sensible, to have a good reproduction quality, you must sample
the sound signal 44100 times per second, with a sufficient
precision level. This series of values is called the time
representation of the sound. It gives the pressure value at any
given time of a music concert. Here is how it appears for
instance in the audio editor window of Pizzicato: A mathematician called Joseph Fourier, established in the 19th
century that such a signal could always be decomposed as a sum of
sine and cosine waves of fixed frequencies and amplitudes.
Practically, this means that the sound of a full orchestral
symphony may be reduced to the sum of a series of simple sine
waves with specific amplitudes and phases, with no variation in
time for the full duration of the symphony. When you think about
it, it is quite fascinating! But do not change a few of the
frequencies or amplitudes, as the symphony may become an obscure
sound confusion. This way of representing a sound of a given time duration is
called the frequency representation, or the frequency spectrum of
the sound. In theory, you can switch back and forth between the
time representation and the frequency spectrum representation and
lose no information in the process (which means, keep the sound
exactly the same). In practice, you can not make this process
with an infinite number of frequencies, so you have to quantize
the frequencies you will analyse and this precision may affect
the sound result. Pizzicato lets you analyse a portion of a sound signal to see
what it represents in terms of frequency. You can then edit these
frequencies (delete some, add some others, modify the spectrum,
filter it,...) and then synthesize the signal back to the audio
window. This is a way of experimenting sound design and
manipulations. We will see now how to do that practically. The spectral analysis window [Professional] [Composition Pro] When you select some portion of a sound in
the audio window (see the lesson on the audio editor window), you
can right click the background of the window and reach the
contextual menu item Spectral analysis... Working on the harmonics of a sound [Professional] [Composition Pro] You can design a new spectrum based on the
harmonic series and then synthesize the corresponding sound. By enabling the first check box, Pizzicato will apply a
filter on the spectrum, based on the note you select in the
above dialog (you can also enter any frequency). This filter
will act to display and use only the integer multiples of the
note frequency. For instance, if you have a note of 220 Hz,
Pizzicato will only enable the harmonics of this note, which
are [220, 440, 660, 880,...]. The Inharmonic factor can be used to detune the
all harmonic construction, as this number will be used to
multiply frequencies. For instance, if you enter 1.1 for that
value, the harmonic will become [220, 220+220*1.1=462,
462+220*1.1=704,...]. The Enlargment of harmonic peak will in fact
extend slightly each harmonic. For instance, if the value is
1 and the precision is 1 Hz in the spectral window, there
will be the presence of the above harmonics but for harmonic
440, there will also be 439 and 441 frequencies, etc... By clicking OK, Pizzicato will filter out any
frequency of the current spectrum that is not in these
specifications. You can then use the pen, eraser and line
drawing tools to design a spectrum and you will see that only
the harmonics as specified in that dialog will appear. You
can for instance draw a spectrum like this, around C1, with a
peak enlargment of 4 : You can then synthesize it back in the audio window and
hear how it sounds like. Then modify, synthesize and hear
again. You may combine this kind of manipulation with the
design of a virtual and modular synthesizer to create and
modify samples of your own sounds.