Bitstream Dac's

They could replace a $40 16 bit DAC with a $2 1 bit Bitstream DAC and 90% of people could not tell the difference.

And this is the reason why R2R Multibit dac chips ceased to be manufactured, because they were too expensive even though they are the more accurate conversion technique.
But they are making a quite a large comeback in "discrete" form from non mainstream manufacturers like MSB, Total Dac, Metrum Acoustics, Holo, Denafrips, Soekris, Aqua LaVoce mk3 ect ect ect

This "could" force the major d/a chip makers (Philips, ESS, Texas, Analog Devices Wolfson, Crystal ect ect) to start producing them again
                                                   WE CAN ONLY LIVE IN HOPE!!

Cheers George

I have a Conrad Johnson Sonographe 22 bitstream CD player. Will this play SACD or other CD formats? 

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).

Some DAC's and CD players went with Dual Mono Bitstream converter setups as well.

My recollection from back when the first bitstream players came out was that the consensus among the critics was (1) Bitstream players were cheaper to make and didn't need to match DAC chips like the so called "ladder" DACs (don't ask me if it's true, I'm just remembering), so in cheaper players where it was too expensive to match the multi-bit DAC chips the bitstream players could have an advantage in that regard, (2) bitstream players generally had a smoother high end, subjectively, than multi-bit DACS but (3) were not as good in the bass as the multi-bit DACs. As time has gone on there have been some outstanding bitstream players and DACs, as well as multi-bit ones, and when you get into the more costly, better engineered designs the differences probably blur. Anyone with a technical bent able to comment?

I am not a techie, but in simple terms, bitstream is just how the signal is processed. They are also called 1 bit converters. It was Philips technology. Instead of a 24bit, 20bit, 16bit etc. data stream, the data stream is broken down into 1 bit pieces and them mixed/sampled up to whatever resolution the techonology could produce. Or put another way instead of a 20 bit data stream, you would have twenty 1 bit pieces of data. The upsampling / oversampling used was called "Continuous Calibration" instead of the 8X oversampling you find in many multibit DACs. It was at time the best way to reduce jitter at a reasonable cost.

Many CD players using bitstream had resolution equivalent to 20 bit. One of the best Philips chips was the TDA1305. You could search the model number to find players and more specs on it. Companys like Naim, Roksan Caspian, Cambridge Audio (their best CD6 and DACMagic), Rotel and others used this chip.

It is old technology, but not yet inferior if coupled with good electronics.