Com 226 comp trouble shooting II theory book
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- 1194 Sound Boards Sound Mic Analog signal Digital signal Software driver Storage device (hard drive) Soundboard hardware FIGURE 41-2 The soundboard recording process.
- The soundboard playback process.
| The Concept of Sampling To appreciate the intricacies of a sound card’s operation, you must understand the concept of digitization (otherwise known as sampling). In principle, sampling is a very straightforward concept an analog signal is measured periodically, and its voltage at each point in 1194 Sound Boards Sound Mic Analog signal Digital signal Software driver Storage device (hard drive) Soundboard hardware FIGURE 41-2 The soundboard recording process. Software driver Storage device (hard drive) Analog signal Digital signal L spkr. R spkr. Soundboard hardware FIGURE 41-3 The soundboard playback process. Time is converted to a digital number. The device that performs this conversion is known as an Analog-to-Digital Converter (ADC). It sounds simple enough in principle, but it has some important wrinkles. The problem with sampling is that a digitizer circuit has to capture enough points of an analog waveform to reproduce it faithfully. The example in Fig. 41-4 illustrates the importance of sampling rate. Waveforms A and B represent the same original signal. Waveform A is sampled at a relatively slow rate—only a few samples are taken. The problem comes when the signal is reconstructed with a Digital-to-Analog Converter (DAC). As you see, there are not enough sample points to reconstruct the original signal. As a result, some of the information in the original signal is lost. This form of distortion is known as aliasing. Waveform Bis the same signal, but it is sampled at a much higher rate. When that data is reconstructed, the resulting signal is a much more faithful reproduction of the original. As a rule, a signal should be sampled at least twice as fast as the highest frequency contained in the signal—this is known as Nyquist’s Sampling Theorem. The lowest standard sampling rate used with today’s soundboards is 11kHz—this allows fair reproduction of normal speech and vocalization (up to about kHz. However, most low- end soundboards can digitize signals up to kHz. Unfortunately, the human range of hearing is about kHz. To capture sounds reasonably well throughout the entire range of hearing, you would need a sampling rate of 44kHz—often known as CD-quality sampling because it is the same rate used to record audio on CDs. The disadvantage to high sampling rates is disk space (and sound file size. Each sample is apiece of data, so the more samples taken each second, the larger and faster a file grows. If 8 bits are used for each sample, 256 discrete levels can be supported. But the most popular configuration is bit conversion, which allows a sample to be represented by one of 65,536 levels. At that level of resolution, samples form a very close replica of the original signal. Many of today’s soundboards are bit. Download 1.89 Mb. Share with your friends:
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