The choice of equipment for a digital audio project will vary depending on the recording formats you are working with and the amount of modification you want to make to the sound signal. A modest course-reserve encoding project based only on compact disc recordings can be put in place with nothing more than a laptop, while a full-blown audio preservation project that includes 78s, LPs, and tapes will require professional-quality audio components to play back the sound as well as additional components to process the audio signal.
Because of the fundamental difference between digital and analog recordings, different processes are used to convert each to digital audio files.5.1 A digital recording--such as a compact disc--already consists of digital audio data, so the process involves simply reading the digital data on the disc and storing it as a file on a computer. This conversion can be done by any computer with a CD-ROM drive that is running CD extraction (or ``ripping'') software. The time needed to extract the audio from a CD will vary according to the speed and throughput of your computer's CD-ROM drive and microprocessor, but because the computer is processing data and not sound, extracting CD audio always takes considerably less time than playing back the audio in real time.
Analog recordings must first be converted into digital data before being stored as a file on a computer. This work is done by a digital audio converter (DAC), which is a component part of the computer's sound card or, optionally, its external digital audio interface.5.2 The analog recording is played back on a traditional audio component--typically a turntable or tape deck--whose output is patched into an amplifier or preamplifier, which in turn is patched into the computer's sound card or audio interface.
The source audio can be modified by additional components and software either during the creation of the digital audio file or afterwards. Some common types of manipulation include eliminating stretches of silence at either end of the recording, adjusting the equalization to boost or suppress certain frequency ranges, or filtering out tape hiss, surface pops on a recording, and other extraneous noises.