Sony PCM-1630 Audio Processor

The Sony PCM-1630 is a digital audio processor for professional use, designed to be used with a Sony BVU-800DA/800DB videocassette recorder, a DMR-2000/4000 digital master recorder or any other Sony professional VTR to create a professional PCM recording and playback system.

The Sony PCM-1630 was the third generation of the Sony PCM-1600 system released in 1978, (and shortly after this the Sony DRE-2000 digital reverb was released) which was followed by the Sony PCM-1610, and ultimately the Sony PCM-1630. The Sony PCM-1600 used a U-Matic format VCR for its transport, connected to external digital audio processing hardware.

The Sony PCM-1600, PCM-1610 and PCM-1630 were widely used for the production and mastering of many of the first CDs in the early 1980s. Once CDs were commercially introduced in 1982, tapes recorded on the PCM-1600 were sent to the CD pressing plants to be used to make the glass master disc for CD replication.

Features

• Two-channel digital audio processor with 16-bit linear quantisation
• Switchable 44.1kHz and 44.056kHz sampling frequencies
• RAR (read after read) for improved reproduction reliability, using optional DABK-1630 board and DMR-4000 recorder
• Newly developed analogue filter for A/D and oversampling digital filter for D/A
• Fully compatible with PCM-1610
• Wide 20-20,000Hz frequency response

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 synchronised with an NTSC composite sync signal from a VTR.

Electronic editing
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 analogue tape.

Emphasis circuitry
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 kHz (for a compact disc and digital audio system). In an external sync mode, the unit is automatically synchronised with either frequency by synchronising 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 analogue audio signal. For example, a 16-bit PCM signal requires an analogue bandwidth of about 1-1.5 MHz (compared to about 15-20 kHz of analogue bandwidth required for an analogue audio signal), and, clearly, a standard analogue 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 analogue 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 colour subcarrier present.)

Most video-based PCM processors record audio at 14 bits quantisation, 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 quantisation 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.

Sony PCM-1630 Legacy
The Sony PCM-1630 remained in Sony’s Professional Audio Catalogue until 1993, by which time mastering studios had started using equipment from manufacturers like Apogee, dCS, and Prism Sound, which offered superior sound quality and higher quantisation and sampling rates. Sony introduced the PCM-9000 Optical Disc Mastering Recorder as a successor, a machine with excellent sound quality. However, its reliance on a proprietary Sony recording format was poorly received by the industry, leading to its limited adoption. In truth, the PCM-1630 was the last great digital audio processor for mastering that Sony produced, and it was used to master hundreds of classic albums during its time.