Tutorials and Topics - Peabody Computer Music

How Digital Audio Worksquality”) has a SQNR of 96 dB, which is quite good—much better than traditional taperecording.In short, the more bits used by the computer to store each sample, the better the potentialratio of signal to noise.Memory and storageWe have seen that the standard sampling rate for high-fidelity audio is 44,100 samples persecond. We’ve also seen that 16 bits (2 bytes) are needed per sample to achieve a goodsignal-to-noise ratio. With this information we can calculate the amount of data neededfor digital audio: 41,000 samples per second, times 2 bytes per sample, times 2 channelsfor stereo, times 60 seconds per minute equals more than 10 megabytes of data perminute of CD-quality audio.For this quality of audio, a high-density floppy disk holds less than 8 seconds of sound,and a 100 MB Zip cartridge holds less than 10 minutes. Clearly, the memory and storagerequirements of digital audio are substantial. Fortunately, a compact disc holds over anhour of stereo sound, and a computer hard disk of at least 1 gigabyte is standard for audiorecording and processing.ClippingIf the amplitude of the incoming electrical signal exceeds the maximum amplitude thatcan be expressed numerically, the digital signal will be a clipped-off version of the actualsound.A signal that exceeds maximum amplitude will be clipped when it is quantizedThe clipped sample will often sound quite different from the original. Sometimes thistype of clipping causes only a slight distortion of the sound that is heard as a change intimbre. More often though, it sounds like a very unpleasant noise added to the sound. Forthis reason, it’s very important to take precautions to avoid clipping. The amplitude of theelectrical signal should not exceed the maximum expected by the ADC.27