Sony SCD-1

Advanced Capacity Variavble Coefficient Digital Filter
The SCD-1 offers excellent playback performance for both CD and SACD formats. The key feature for this high quality sound for the CD format is the 24-bit precision variable digital filter (VC24).
Compared to conventional VC type digital filters, the VC24 handles twice as many operation steps, has a 24-bit word length, as opposed to 22, and performs direct 8 times oversampling at a 16-bit word length (3-bits longer) all in one mode. Compare this with the number of bits which can actually be processed within the alloted time span and the result is 2 x 2 x3 = 12 times the number of operation steps. Furthermore, when the bit rate is represented in standard form, that is in a 10-digit system, 2 bit becomes 2²2 for 4 times the number of operation steps and 3 bit becomes 2²3 for 8 times the number of operation steps. Therefore, the total sampling rate is 2 x 4 x 8 = 64 times the number of operation steps. This significant increase in in computing capacity over conventional VC digital filters allows the VC24 to deliver improved CD quality reproduction.

Conventional equipmen,t generally uses a standard digital filter. And in accordance with sampling theory, the fundamental principle in digital audio, this type of filter abruptly cuts the band range over 20kHz.
The df-1 filter is responsible for smoothing interpolation computations during 8 times oversampling. In the past, because of limitations in computing capability, 8 time oversampling was achieved by performing 2 times oversampling three times. Thanks to VC24's capabilities, direct 8 times oversampling is performed simultaneously. The result is smoother processing and therefre cleaner sound quality.

The idea behind the df-2 filter is quite simple. With the objective of being able to perform more sophisticated computations than standard digital filters, as much as possible, the df-2 takes the longest number for calculation processes. Conventional filters have to use truncation (rounding to significant numbers) or rounding up and down in order to pass the data on to the next stage. Instead, the df-2 filter adjusts the length of the input number to match the noise shaper in the next stage. This way, all non-linear portions in the computation process are eliminated. Thus, no quantisation noise is generated and the data read from the CD retains all of its integrity. Also, thanks to the direct 8 times oversampling, there are no longer any non-linear computations between stages, enabling powerful sound.

The df-3 is a completely new type of filter. It is an even number digital filter with direct 8 times oversampling and, by taking advantage of the VC24's advanced operation capabilities, a 224-order filter. Even number filters use a completely different computation process from conventional odd number filters. For example, when performing 8 times oversampling, an odd number filter does not process the original data read from the CD. Instead, it makes computations using the interpolation data, which is a sample of 7.
In th case of this even number filter, computation processes are made using the original data read from the CD and similarily using the interpolated data from the 7 samples. Again, thanks too the VC24's superior computing abilities, the 224-order filter enables flat amplification characteristics from 0Hz to 17kHz, regardless of whether it is a slow roll off type filter or not. Also, this filter enables cutoff characteristics of over 26kHz and performance over 80dB, for extremely high quality. The result is sound that is clear and full of sbtleties.

The df-4 position is based on df-2, with performance enhancements. The computation word length is increased by 4 bits, and the filter degree is increased twofold. As with df-3,, it also uses an even number filter. These specifications allow df-4 to achieve a flat frequency characteristic up to 18kHz and a 20kHz gain. The df-4 reproduces fresh, energetic sound that is full of complexities.

Low-Pass Filter
The current pulse output from the D/A converter is I/V converted, and finally passed through the analogue low-pass filter in the final stage to become an analogue audio signal. The SCD-1 uses a GIC-type low-pass filter, which is different from usual active-type in that the signals are not passed through semi-conductors, or active elements, such as the OP amplifier. This way, the GIC-type filter is able to maintain a high degree of sonic integrity and pure sound quality.

In the SACD system, playback frequency is not determined by the format. Instead, it depends on the cutoff frequency and cutoff characteristics of the low-pass filter on the player side. Therefore, maximising reproduction sound quality requires consideration of numerous factors. Among them are the balance between increased bandwidth and the elimination of quantum noise, as well as filter characteristics such as circuit formats, number of stages, and finally, component element. [...]
Conventional amplifiers and speakers were designed using an approximated 20kHz frequency range characteristic. Assumming that the SCD-1 could be used with such equipment, the frequency range in the standard position has been set to roll off slowly at about 50kHz, creating a curve that satisfies DSD signals, which are apt to exceed 100kHz. Combine the SCD-1 with the TA-E1 and TA-N1 and, using the custom position, enjoy an even more expanded frequency range.