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September 10, 2009

1. instrumental/harmonic: Guzheng

This recording is of a guzheng (chinese zither) G3 string being plucked, i.e. starting a specific pitch on a musical instrument and decaying in volume. In the spectrogram, a high frequency resolution allows us to see a well-defined fundamental frequency at approximately 139Hz with several supporting frequencies especially at the attack of the note. Linear scale shows equally spaced and sized lines to illustrate the harmonic nature of the note. The spectrum is vertically zoomed and stretched at a relatively high sampling rate in order to show clearly the equally spaced peak amplitudes at the fundamental frequency.

2. sharp attacks/short sounds: Hammer

Metal hammer repeatedly hitting a piece of metal on top of metal on a wooden table. There are no clear peak amplitudes in the spectrum to indicate harmonic frequency but instead a dense combination of many across the whole range of frequencies to simply sound like noise. In this case, the spectrogram is therefore more useful with a high time resolution and lower frequency resolution in order to show crisp constrasts in the vertical edges of each hit, telling us when each hammer attack occurs. It is interesting to note that this example is marred by one frequency at approximately 16k, the sound of air conditioning, seen as a peak in spectra and a thin horizontal line in spectrogram. I can’t hear it but Jakes can! tsk tsk.

3. inharmonic: Spoon

Heavy metal spoon being hit with metal scissors. Same analysis choices as the guzheng in order to show good frequency resolution. However, unlike an instrument the inharmonic nature of this object produces no fundamental frequencies. There are strong frequencies both low and high with other frequencies at uneven intervals in between. This is also shown in the spectrum with irregularly spaced peak amplitudes across a larger range of frequencies.

4. bird: Songthrush

Spectral analysis of a bird showed that each note in his song is very small, short, and intense cluster around one frequency. This produces the pureness of this sound as opposed to the resonance of an instrument.


One Comment leave one →
  1. September 13, 2009 5:49 pm

    Very nice.

    For the bird song, since it is quite long, it would have been better to just show a small part. Then we would be able to see the fundamental frequency in some of the notes.


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