Analysis and Delivery
Audio Technology / Recording / Recording Devices / Digital recorders...
Digital recorders are becoming more and more common. They come in a variety of flavors, such as DAT, minidisk, solid state PC card, CD, and hard disk. What distinguishes them from one another are the recording medium and the recording format. For the purposes of acoustic analysis, one should use digital recorders that capture sound in an uncompressed, PCM (pulse code modulation) format.
At the heart of a digital recorder is the Analog-to-Digital converter (ADC). In digital systems, the analog audio signal must first be converted to digital form before it can be further processed. This entails sampling the signal at very short, successive time intervals and converting the value of the sample to a binary number representing the amplitude of the waveform at that instant. The output of the ADC is a series of digital words, typically at a rate of 44,100 words per second (sample rate). Each word contains a certain number (typically 16) of bits (binary digits). The sample rate and bit depth are the most important factors determining the accuracy of the digital representation of the analog waveform.
The most typical digitization settings (so-called CD quality) of a 44,100 Hz sample rate and a 16-bit word length render a recording that has a broad frequency response (about 21,000 Hz) and an impressive dynamic range of 96 dB. Many modern ADCs are capable of sampling at the rate of 96 kHz and a 24-bit resolution, which produces a highly accurate signal with negligible quantization noise. After the signal has been quantized the values of each sample have to be stored on the storage medium that the recording device happens to be using.