Electronic Sound Reproduction
by Ron Kurtus
Since the waveforms of sounds made by musical instruments and the human voice are very complex, it is often difficult for electronic devices to accurately reproduce those sounds.
The complexity of waveform can be illustrated as a graph, comparing the volume of the different frequencies or tones. During the detection process, the waveform may be distorted. Then when the sound is reproduced through loudspeakers, it may be distorted even more.
However, there are ways to improve the quality of the sound.
Questions you may have include:
- How can you show how complex sound is?
- How does sound get distorted when it is detected?
- What happens when you try to reproduce a sound?
This lesson will answer those questions. Useful tool: Units Conversion
Showing sound complexity
A tuning fork is supposed to give off a pure tone of one frequency or note. Hearing a tuning fork is like looking at an object that is only one color. But just like most objects are multicolored, the sounds coming from most objects are very also very complex.
Use a graph
One way to illustrate this is by the use of a graph. The sound from a tuning fork is only one frequency. The height of the bar indicates how loud the note is. The higher the bar, the louder the note is. With the sound from your voice, from a musical instrument or from some other source is highly complex, consisting of many frequencies at different amplitudes or loudness.
The chart below illustrates the loudness of the different frequencies or notes in a complex sound. The height of each bar indicates the relative loudness or amplitude of that frequency.
Chart 1: Simple example of a complex sound
A tuning fork would consist of only one bar or note. Of course, a true sound would have many more frequencies. The hearing range of humans, which is between 20 Hz and 20,000 Hz. (Hz is the abbreviation for Hertz, which means cycles per second.)
Your ear filters that sounds before the reach the brain. In other words, your ear does not record the sound exactly as it was transmitted. Some frequencies or notes may be attenuated or reduced in volume, while others may be recorded exactly as they are.
Microphone can change sound
Likewise, when a microphone records a sound, the some of the frequencies may be attenuated. This is especially true with inexpensive microphones. Such a microphone can severely distort the sound. One good example of a distorting microphone is the mouthpiece in most telephones.
Example of attenuation
This chart below shows how the various notes are reduced in volume due to the attenuation from a microphone. The yellow represents the new sound.
Chart 2: Attenuation of a sound by a microphone
After the microphone detects the sound, it goes through some electronics and is then reproduced and transmitted through loud speakers or headsets that consist of tiny speakers. Just like a microphone, the speakers also attenuate various frequencies and distort the sound coming out.
Even more attenuation
The chart below shows how the sound has changed due to attenuation from the microphone and then the speaker. Note that the highest frequency cannot be heard at all.
Chart 3: Attenuation of a sound by a microphone and speaker
Good speakers more faithful
Well-made speakerswhich are usually more expensiveare the most faithful in reproducing the sound signal they receive. Since they often must produce amplified sound, speakers often have difficulty faithfully reproducing all frequencies.
That is why better stereo systems have several types of speaker cones in one speaker box. They may have a tweeterwhich is good at reproducing high notesand a bass speaker for the lower frequencies.
Can adjust with equalizer
Some expensive car radios and stereo systems have what are called "equalizers" that show the volume of the different frequencies with rows of lights. Equalizers allow you to adjust the volume of these individual frequencies to overcome the attenuation of each note. This results in a sound that is closer to the original sound.
Sounds from your voice or music are highly complex. There is distorting or attenuation of frequencies in the detecting and reproducing processes. Thus, the music you hear from the radio is never quite as good as if you would hear the original, live sound.
Help others learn more about the characteristics of sound.
Resources and references
Sound Reproduction - Information from Linkwitz Lab design and consulting
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Electronic Sound Reproduction