Bitstream DACs have evolved into todays Delta-Sigma DACs. They increase the conversion frequency while they reduce the number of bits they convert. This results in single and multibit Delta-sigma DACs. The more bits in the final conversion the more expensive (and higher resolution) the DAC.
Bitstream DACs of only one bit can recreate low frequency signals very accurately but high frequency signals suffer. However the human ear becomes less sensitive to distortions at high frequency so Delta-Sigma DACs sound good because they are naturally psycoacoustically matched to human hearing.
If a bitstream DAC is to reproduce a signal with the exact same resolution as the original then it must double the sampling rate for every bit it drops from the signal. A 44.1Khz CD would need a conversion frequency of 1.445Ghz at 1 bit (2^15 or 32768 times 44.1Khz) to match the 16 bit origional. This is too fast to be practical. It has however been found that acceptable sound is achievable with only 64 or 128 times the origional. The best Delta-Sigma DACs use a combination of 64 or 128 times oversampling and multiple bits (Like the Burr-Brown PCM1716 128 times oversampling and 4 bit conversion). The early bitstream DACs used only 64 times oversampling and 1 bit conversion and did not sound as good as other DACs at the time but they were really cheap so the manufactures loved them. They could replace a $40 16 bit DAC with a $2 1 bit Bitstream DAC and 90% of people could not tell the difference.
SACD is a pure bitstream format. It is simply a CD resolution digital signal that is already formatted in Delta-Sigma (Bitstream) format. In fact if you were to compare the resolution in the 2.8Mhz 1bit SACD format and a 44.1Khz 64 times Delta-Sigma DAC you would find them identical. SACD is simply 44.1Khz x 64 = 2.8224Mhz (look at Sony's Documentation and you will find this number).
Bitstream DACs of only one bit can recreate low frequency signals very accurately but high frequency signals suffer. However the human ear becomes less sensitive to distortions at high frequency so Delta-Sigma DACs sound good because they are naturally psycoacoustically matched to human hearing.
If a bitstream DAC is to reproduce a signal with the exact same resolution as the original then it must double the sampling rate for every bit it drops from the signal. A 44.1Khz CD would need a conversion frequency of 1.445Ghz at 1 bit (2^15 or 32768 times 44.1Khz) to match the 16 bit origional. This is too fast to be practical. It has however been found that acceptable sound is achievable with only 64 or 128 times the origional. The best Delta-Sigma DACs use a combination of 64 or 128 times oversampling and multiple bits (Like the Burr-Brown PCM1716 128 times oversampling and 4 bit conversion). The early bitstream DACs used only 64 times oversampling and 1 bit conversion and did not sound as good as other DACs at the time but they were really cheap so the manufactures loved them. They could replace a $40 16 bit DAC with a $2 1 bit Bitstream DAC and 90% of people could not tell the difference.
SACD is a pure bitstream format. It is simply a CD resolution digital signal that is already formatted in Delta-Sigma (Bitstream) format. In fact if you were to compare the resolution in the 2.8Mhz 1bit SACD format and a 44.1Khz 64 times Delta-Sigma DAC you would find them identical. SACD is simply 44.1Khz x 64 = 2.8224Mhz (look at Sony's Documentation and you will find this number).