Computer Sound
This article traces sound
from a file stored on the computer hard drive to the conception in our mind of
sound.
Suppose we want to play a midi file stored on our computer using an external sound system. Here are the steps involved.
1. We use a program called “media player” to play the midi file 'Blue Bells of Scotland.mid' which you should hear now and which I played on my synthesizer keyboard and recorded as a midi file on my computer. A midi file, or “Musical Instrument Digital Interface,” file contains note data much like a music box wheel or a player piano paper roll. There is no sound data, just data on what sound to make. The program sequences the midi data and sends it to WINDOWS. The picture above shows that the program "media player" is "playing" the file "Tom Sawyer.mid" The background picture is how WINDOWS is visualized on the screen.
2. Windows knows what to do with the midi data; that is, where to place it; or in other words, what data port to send it to so that it will be output to the external midi device. The picture above shows the midi output plug in the game port on the back of the computer.
3. The midi data is sent to a Midi Patcher, a device that sends the data to selected midi instruments. The above picture shows that the data coming from device 1 (the computer) is being sent to devices 2 and 5. These devices are synthesizer keyboards.
4. The midi synthesizers receive the digital data and convert it to analog sound. Most ‘synthesizers’ today just use stored digitized sound to create analog sounds. Older synthesizers used electronic devices to actually synthesize sounds. The top picture is of a Yamaha PSR-510 synthesizer, device 2, and the lower picture is of a PSR-SQ16 synthesizer, device 5.
5. The analog sounds produced by the synthesizers are sent to a mixer, which combines the separate sounds into one sound. The above picture is of my mixer/amplifier device. The left portion shows the mixer device controls, and the right portion shows the amplifier device controls.
6. The mixed sound is sent to a Digital Signal Processor, or DSP device. This computing device takes the analog sound through several steps. First the analog sound is converted back to digital sound by an AD (Analog to Digital) converter. Then a mathematical process called a Fourier Transform separates out the elemental sound frequencies and amplitudes of the sound into numbers. Then the frequencies and amplitudes are processed to form echoes, doubling, reverberations, and other sound effects. The resulting numbers go through an Inverse Fourier Transform to be converted back to digital sound. Finally, the digital sound is converted back to analog sound using a Digital to Analog (DA) converter.
7 The sound then goes to an amplifier. The picture is above.
8 The amplified sound goes to the ‘speakers’ which change the analog electrical impulses to sound waves in the air.
9. Our ears pick up the sound air waves.
10. Finally, the most remarkable part of the whole process occurs. The sound waves in the air strike our eardrums, and through a complex process, which might operate somewhat like the DSP device described above, changes the vibrations of our ear drums into intelligible sound. What is remarkable is that we can ‘hear’ many sounds at once. We can discern music, a conversation, and extraneous sounds, like a motorcar outside the room, all at the same time.
When I finished my studies at Lynchburg College I wrote an honors paper in order to graduate Magna Cum Laude with a BA in mathematics. My paper was on Fourier Transforms. When I got my first computer I soon learned how to use it to produce sounds and music, writing programs in assembly language. Then I turned to Fourier Transforms, writing programs to do the direct and inverse transforms. The critical test of the programs was that the data put into the two steps was close to the same as the data that came out.
I used the computer to configure sound waves and to help compose music for the computer to play. Here is an example of "Computer Music." Click the link below. It lasts three minutes.
Color Computer music.