Sony SCD-1

The D/A Converter System : S-TACT
The Synchronous Time Accuracy Controller (S-TACT) pulse generator reads the pulse code data and forms the pulse waveform accordingly. The pulse is formed using the clock generator, which is controlled by a quartz oscillator. For this reason, the pulse formed using S-TACT is extremely precise, and therefore generally referred to as quartz precision. Conventional systems incorporate digital calculating devices like a noise shaper on the clock generator side. The SCD-1 completely separates them in order to eliminate the infkuence from digital noise.

Signal processing carried out in the digital operation stage is performed at a speed 512 time faster than the sampling frequency for CD. This is equivalent to 8 times the sampling frequency for SACD. which is performed at a capacity of over 50 bits. During these operations, the switching noise emitted by the transistor element in the LSI IC is considerable. The actaul amount of switching noise is dependent on the audio signal being processed. This noise enters the power supply and creates voltage fluctuations, resulting in a loss of precision in the time axis when the pulse is being formed. As jitter is introduced into the pulse, the precision of the original signal is degraded.
S-TACT on the other hand, uses a discrete construction to completely separate digital operations from pulse formation. As a result, it becomes possible to create a pulse that achieves quartz precision for the time axis. Making use of of this technology, SACD is able to provide higher quality playback for improved audio software.

Current Pulse D/A Converter
The current pluse D/A converter converts the voltage pulse output from the S_TACT pulse generator into a current pulse. However, in the case of the voltage pulse signal, the height of the pulse can be slightly affected in the form of fluctuations during switching response. Taking this into account, the SCD-1 incorporates a D/A converter for accurately reproducing these pulse signals. Using an exceptionally stable and constant power supply, the SCD-1's D/A converter converts voltage pulse to current pulse and thereby enhances the precision of amplitude axis direction.