Page 162 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Unit 7: Graphics and Multimedia

(2 to the 8th power). Sampling at 16-bits divides the voltage into 65,536 parts (2 to the 16th power). Notes
Using a higher sampling resolution creates cleaner recordings with less background noise. Higher
sampling resolutions also capture a wider dynamic range. For example an 8-bit digitizer will only
capture sounds up to 48 decibels (DB). Any portion of the sound that is louder than48 DB will be
clipped and the resulting sample will sound distorted. 16-bit digitizers, however, capture up to
96 DB of volume. The dynamic range of the human ear extends to 120 DB.
Quantization is the term that describes the process of measuring the amplitude of a sound and
rounding off the measurements according to the sampling resolution. For example, an 8-bit sound
digitizer will assign integer values of between 0 and 255 for the amplitude of each sample. The
result is that the original smooth waveform is reconstructed as a staircase shape with only 256
discrete levels of amplitude and noise is introduced into the signal. 16-bit digitizers, on the other
hand, assign amplitude values on a scale of 0 to 65,535. At that level of precision, the reconstructed
waveform is almost identical to the original and almost no noise is introduced.

Figure 7.6: Original Waveform and Quantized Waveform

All of these measurements are made by an analog-to-digital converter. The measurements can
then be stored as binary numbers in a file on a computer’s hard disk. To play back the sound,
the computer sends the information in the file to a digital-to-analog converter which reproduces
the original electrical signal. That signal is then sent to a speaker which produces the sound as
described earlier.
Maximum precision per measurement combined with maximum sampling rates produces
the highest quality recordings. To describe a digital recording of a sound, therefore, one
can speak of the sampling rate and resolution. For example, sound recorded at a sampling
rate of 22 kHz with 8-bit resolution is considered to be of a quality similar to that of a
telephone call. Sound recorded at 44 kHz and 16-bits is considered the minimum quality for
compact disc recordings because it captures the full range of human hearing. In multimedia
production work, 11 kHz, 8-bit sound is sometimes acceptable for speech recordings
and 22 kHz, 8-bit resolution or 11 KHz, 16-bit resolution is often considered acceptable
for music. For the highest-level multimedia work, however, nothing short of 44 kHz,
16-bit sound is acceptable.
When sound waves strike a microphone, they are converted to an electrical signal which
is measured many thousand times per second by an analog-to-digital converter chip. The
measurements are stored in the computer as binary numbers.
The higher the quality of sound, the more space it takes to store the sound. A compact disc can
store about 74 minutes of stereo sound at 44 kHz, 16-bit. If you reduce the quality to 22 kHz, 8-bit
stereo sound, however, you can store approximately 300 minutes of audio on the same disc. In
other words, one minute of stereo sound takes 10 megabytes of storage at 44 kHz, 16-bit quality,
and only 2.5 megabytes of storage at 22 kHz, 8-bit quality. When producing sound for multimedia,
therefore, one must consider not only sound quality, but also how the sound will be distributed.
If your multimedia program will be distributed on CD then you may have enough storage space

LOVELY PROFESSIONAL UNIVERSITY 155