Sony PCM-1630 High Performance recording and playback
The PCM recording and playback system, including the Sony PCM-1630 and recorders such as a DMR-2000/4000 and a BVU-800DA/DB, gives high performance with the following characteristics:
- Number of channels: 2 channels
- Modulation system: PCM system conforming to the NTSC standard television system
- Sampling frequency: 44.1kHz or 44.056kHz
- Frequency response: 20HZ to 20 kHZ (+0.5/-1.0 dB)
- Dynamic range: More than 90dB
- Harmonic Distortion: less than 0.05% (at reference input level)
- Wow and flutter: below measurable limit
Digital dubbing with no deterioration
When the unit is connected to two recorders, sound can be dubbed digitally with no deterioration, due to the digital dubbing function of the unit.
Synchronisation with video equipment
The unit can be synchronized with an NTSC composite sync signal from a VTR.
When the unit is used with a DAE-1100/1100A digital audio editor and two recorders, a program can be automatically and electronically edited with precision, and the quality of the editing is more excellent than splice-editing of an analog tape.
The built-in emphasis circuit improves the ratio of high frequencies by raising their recording level and lowering their playback level.
Serial data format and interchangeability
A serial data format is employed as a digital input/output format. Since this format is interchangeable with that of a PCM recording and playback system using a Sony PCM-1610 digital audio processor, it is possible to directly transmit and receive digital data between this unit and the Sony PCM-1610 system.
Tapes recorded with this unit can be played back with a Sony PCM-1610, and vice versa. This unit can be used instead of a PCM-1610 in a PCM recording and playback system using a PCM-1610. (The remarkable difference in the two units is that the PCM-1630 does not incorporate a time code generator, while a PCM-1610 has a built-in time code generator)
Two sampling rates selectable
A sampling rate is selectable for recording at either 44.056 kHz (corresponding to the NTSC TV system) or 44.1 kEZ ( for a compact disc and digital audio system). In an external sync mode, the unit is automatically synchronized with either frequency by synchronizing with an NTSC composite sync signal or a word sync signal.
Linear phase response
To improve the phase response, phase compensation filters are incorporated in the A/D section, and over-sampling FIR ( finite impulse response) filters are incorporated in the D/A section.
How it works
A PCM processor is a device that encodes digital audio as video for recording on a videocassette recorder. The adapter also has the ability to decode a video signal back to digital audio for playback. This digital audio system was used for mastering early compact discs.
High-quality PCM audio requires a significantly larger bandwidth than a regular FM analog audio signal. For example, a 16-bit PCM signal requires an analog bandwidth of about 1-1.5 MHz (compared to about 15-20 kHz of analog bandwidth required for an analog audio signal), and, clearly, a standard analog audio recorder could not meet that requirement. One solution arrived at in the early 1980s, was to use a video tape recorder, which is capable of recording signals with this high bandwidth, to store the audio information, but a means of converting the digital audio into pseudo-video was necessary.
Such an audio recording system therefore includes two devices, namely the PCM processor , which converts audio into pseudo-video, and the video tape recorder itself. A PCM processor has the analogue audio (stereo) signal as its input, and translates it into a series of binary digits, which, in turn, is coded and modulated into a monochrome (black and white) video signal, appearing as a vibrating checkerboard pattern, modulated with the audio, which can then be recorded as a video signal.
This video signal can be stored on any ordinary analog video tape recorder, since these were the only widely available devices with sufficient bandwidth. This helps to explain the choice of sampling frequency for the CD, because the number of video lines, frame rate and bits per line end up dictating the sampling frequency one can achieve, that sampling frequency of 44.1 kHz was thus adopted in the Compact Disc, as at that time, there was no other practical way of storing digital sound than by a PCM Converter & video recorder combination.
The sampling frequencies of 44.1 and 44.056 kHz were thus the result of a need for compatibility with the 25-frame (CCIR 625/50 countries) and 30-frame black and white (EIAN 525/60 countries) video formats used for audio storage at the time. (Note that neither PAL nor NTSC was itself used, only the luminance signal, or black and white information, of the composite video output from the PCM processor was used with no color subcarrier present.)
Most video-based PCM processors record audio at 14 bits quantization, and a sampling frequency of 44.056 kHz for EIAN countries (or 44.1 kHz for CCIR countries.) However, some of the earlier models, such as the Sony PCM-100, recorded 16-bits quantization as well, but used only 14 of the bits for the audio, with the remaining 2 bits used for error correction, in case of dropouts or other anomalies being present on the videotape. A PCM adaptor can only store a single stereo signal, and is not capable of studio multi-track recording.
Shortly after the arrival of the Sony PCM-1630, an integrated system was developed, known as DAT (Digital Audio Tape) which did not require the external VTR to record, instead it used an inbuilt 4mm wide taped based helical scan system, which all but wiped out these larger PCM-1600 systems.