After reviewing and analyzing the different spectrogram graphs through the experiments, I still did not understand why the graph did not look like a single horizontal line as it was playing one frequency. I understood that overtones were graphed, but I did not understand how they were produced. This reminded me of Edison’s phonograph, and the tin-foil film and how it would be indented with a needle on a diaphragm. But I asked myself how could it tell the difference between the sound of a voice and of a cornet if both were singing and playing the same frequency. I now found the answer.
Though the spectrogram graphs I used in my experiments generated through audacity are different from the graph from Musical Instruments, they can be read the same way. In Musical Instruments, the higher the vertical wave, the higher the amplitude. In Audacity, ranging from blue-red-white, the whiter the colour, the higher the amplitude. In the first graph shown below there are 2 amplitude peaks at different points of frequency, or strong frequency regions. These are called formants.
Even though 2 different instruments can be playing the same frequency, there can be a distinction between the 2. Refer to the diagrams below and how the components along the frequency axis are evenly spaced apart. This spacing is the fundamental frequency, hence the same note or pitch. However, from different people and instruments, there will a different formants and different wave-forms. These differences determine the difference in colour of sound, timbre and quality of sound. At the moment, I cannot find any difference between these 3 terms.
References and Reading material
- Fauvel, John, Flood, Raymond, and Robin Wilson. Music and Mathematics, New York, Oxford University Press, 2004. p 55-56
- Campbell, Murray, Greated, Clive, and Myers, Arnold. Musical Instruments History, Technology & Performance of Instruments of Western Music, New York, Oxford University Press, 2007. p 35-36