Audio Technology / Recording / Recording Devices / Minidisk recorders...

Minidisk recorders are quite popular among field workers, particularly due to their small size and ease of use. However, most minidisk recorders do not produce the quality required for detailed acoustic analysis. First of all, most of the portable minidisk recorders lack a quality pre-amplifier, which makes it difficult to interface them with premium-grade microphones. Minidisk field recordings are usually shipped with small, inexpensive lavalier condenser microphones whose frequency response and dynamic range are typically rather poor. In addition, there is virtually no control over the incoming signal. The A/D converter is inferior to that found on larger DAT or hard disk recorders.

Many portable minidisk recorders lack the S/PDIF I/O interface, which makes it necessary to use a standalone minidisk deck for digital audio transfer. Finally, to achieve a small disc diameter, MD uses data reduction based on psychoacoustic principles. Prior to storage, the audio data rate (bit rate) of 1.41 Mbps (uncompressed PCM) is compressed using a perceptual coder (proprietary algorithm developed by SONY) to lower the bit rate to 292 Kbps (1/5 of the original). ATRAC preserves the sample rate (44,100 Hz), but decreases the word length (resolution), which results in a less faithful representation of the analog original and quantization noise, which is then masked by the algorithm, yet, technically it is still there, though we can't hear it. A lower word length, naturally, results in decreased dynamic range, which, of course, the algorithm cannot compensate for. As a result, we have a recording that has the full 20-20000 Hz frequency response, but has a decreased resolution, increased quantization noise, and decreased dynamic range.