HDCD player with 18bit DAC? How? (1 Viewer)

[David Ely]

Okay, I'm a little confused.
If I usderstand HDCD correctly, it includes 4 extra bits of information. This will allow 20-bits of information on an HDCD. There are a lot of HDCD players on the market (Denon 370 being the most popular) that have 18-bit DACs. Isn't this totally defeating the purpose of HDCD? Aren't you going to loose 2 of the extra 4 bits within the DACs?

 

[David Ely]

Anyone?

 

[Saurav]

I'm not sure the data word length (or width, if you will) and the number of bits in the DAC have a one-to-one correspondence. For instance, I've seen CD players with 1-bit DACs, and some feel that 1-bit DACs sound better than multi-bit DACs. Obviously, a 1-bit DAC has some way of handling the 16 bits of regular PCM audio. This probably works by accumulating bits in some way, instead of reading in the whole word in parallel and generating the analog value based on that.

 

[Kevin P]

I'm not sure the data word length (or width, if you will) and the number of bits in the DAC have a one-to-one correspondence. For instance, I've seen CD players with 1-bit DACs, and some feel that 1-bit DACs sound better than multi-bit DACs.

There's many ways to skin a DAC (

) but the two most common ways are:

• Multi-bit DAC - basically each bit in the "word" is applied to a gate that outputs a voltage for a 1 or no voltage for a zero--these voltages are fed into a voltage divider and then to an output amp. Each higher-end bit produces twice the voltage of its lower bit. Add them all together and you get an analog signal corresponding to the value of the "word" being applied to the DAC. A 16 bit converter would have 16 gates and 16 elements in the voltage divider.
• 1-bit DACs take the input word and output a stream of high-speed pulses, the width/frequency of which depends on the value being input. The pulses are then "averaged out" to an analog signal via a low-pass filter. The "on" time of the output pulse depends on the value being converted; for example, a value in between zero and maximum (50%) would output a waveform which is on 50% of the time and off 50% of the time, which would average out to half of the maximum output level of the analog signal after filtering.

I don't know the technical specifications of HDCD, but maybe it adds "up to" 4 additional bits of information (some compression is likely involved). Perhaps an 18-bit converter is a happy medium that saves some cost but still provides additional resolution over standard CD.