What is a 1-bit DAC ?

[percy]

sorry if its a dumb question (not big into digital yet) but why does my Sony discman say "1bit dac" ? AFIK a regular audio cd is encoded using 16-bits so I'd believe it would need a 16bit decoder(?). What is this 1bit dac then ?

[ghetto]

http://electronics.howstuffworks.com/question620.htm

If you google for "1 bit dac" you'll find many more in depth explanations and circuits even

[phn]

For what it's worth, the SACD uses a 1-bit DAC as well. The DSD technology of the SACD has a higher sampling rate but lower resolution than the CD, at least above 10khz. So much for "hi-rez," eh?

[ThorstenL]

Konnichiwa,

Originally posted by percy
sorry if its a dumb question (not big into digital yet) but why does my Sony discman say "1bit dac" ? AFIK a regular audio cd is encoded using 16-bits so I'd believe it would need a 16bit decoder(?). What is this 1bit dac then ?

A 1 Bit dac is expressed in the simplest terms a Device that uses a form of pulse width modulation to generate an output signal proportional to a digital input.

Consider it like this:

A squarewave is output at exactly 50% Dutycycle.

Lowpass filter this squarewave and you get a volage equivalent to 1/2 the peakvoltage.

Vary the duty cycle to say 25/75% and your output voltage is 25% the peak voltage.

You can now use a digital mechanism to genertae sucha waveform by varying the pulse width according to a given system.

For example, if we used a clock at 256 Times that of the sample clock we could make for each sample value 256 discrete values simply by varying the width of the output pulse at the sample rate.

Therefore a 1-Bit dac to operate at 16B bit equivalent resolution must operate at 65536 times the sample frequency, in short at GHz frequencies. This is clearly not possible.

Therefore ANY 1-Bit (or delta/Sigma) DAC has a real resolution much lower than 16-Bit and uses a number of mathematical and psychoacoustic tricks to make up for that.

Usually the tricks do not work well causing a very distinct type of sound to appear. This type of sound is either liked or not.

More recent approaches combine Multibit DAC's of low resolution (4 - 8 Bit) with 8 Bit equivalent resolution capable 1-Bit and add noiseshabping to get reasonable performance. These are usually called "Multilevel Delta Sigma" and are a better choice.

Sayonara

[Bernhard]

Originally posted by Kuei Yang Wang
For example, if we used a clock at 256 Times that of the sample clock we could make for each sample value 256 discrete values simply by varying the width of the output pulse at the sample rate.

Therefore a 1-Bit dac to operate at 16B bit equivalent resolution must operate at 65536 times the sample frequency, in short at GHz frequencies. This is clearly not possible.

Therefore ANY 1-Bit (or delta/Sigma) DAC has a real resolution much lower than 16-Bit and uses a number of mathematical and psychoacoustic tricks to make up for that.

Usually the tricks do not work well causing a very distinct type of sound to appear. This type of sound is either liked or not.

I wonder why two of the better bitstream players which I own have low noise like PCM63 players and even lower distortion at -60dB.

By the way 2 PCM63-J and 2 PCM63-K2 chips I recently tested, all were not better than randomly selected PCM56 and have been totally outperformed by very good PCM56 chips.

Question:

R2R-ladder DACs have a number of resistors that depends on the number of bits.
Compared to a 16 bit DAC, statistically it is more likely that a 20 bit DAC got resistors that do not match the desired value, leading to nonlinearity of the DAC chip.
Even more if it is a "colinear" DAC

Other question:

How got Philips 16 bit out of a 14bit 1540 DAC ?
averaging bits / 4 samples ?

[ThorstenL]

Konnichiwa,

Originally posted by Bernhard
I wonder why two of the better bitstream players which I own have low noise like PCM63 players and even lower distortion at -60dB.

First, Delta Sigma eliminates the distortion sources common to multibit DAC's. Therefore distortion according to conventional measurements will not exist. Noisefloor depends upon many factors. Have you ever done a noiseload test?

Conventional measurements show very little relation to "subjectively percieved good sound".

Originally posted by Bernhard
Other question: How got Philips 16 bit out of a 14bit 1540 DAC ? averaging bits / 4 samples ?

In essence yes. They used primitive noiseshaping and 4 X Oversampling to add in effect 4 more discrete values to the output, in other 2^2 or 2 Bits.

Sayonara

[Bernhard]

Originally posted by Kuei Yang Wang
Have you ever done a noiseload test?

Conventional measurements show very little relation to "subjectively percieved good sound".

I use -60dB dithered and noiseshaped signal from a forum member.

What I observe is that DACs with visible distortion tend to sound more warm, brilliant or harsh or all together, while clean DACs sound more detailed, smooth and colder /more neutral.
With exceptions like TDA1540 in CD304 which sounds neutral too, and my very clean CD880 which sounds "yellow".

So for me there is already a relation between measurement and sound.

[percy]

Originally posted by Kuei Yang Wang
For example, if we used a clock at 256 Times that of the sample clock we could make for each sample value 256 discrete values simply by varying the width of the output pulse at the sample rate.

Therefore a 1-Bit dac to operate at 16B bit equivalent resolution must operate at 65536 times the sample frequency, in short at GHz frequencies. This is clearly not possible.

Therefore ANY 1-Bit (or delta/Sigma) DAC has a real resolution much lower than 16-Bit and uses a number of mathematical and psychoacoustic tricks to make up for that.

Ok. So what is the difficulty in implementing a true 16-bit dac ? (the 'how stuff works' link above tried to explain that but it went over the top).

More recent approaches combine Multibit DAC's of low resolution (4 - 8 Bit) with 8 Bit equivalent resolution capable 1-Bit

I think I understood the part about Multibit DAC's of low resolution (4-8 bit) in the sense that it must be allowing to use a lower (than Ghz) frequency, right ?
But I didn't understand the part about combining it with '8 bit equivalent resolution capable 1-bit'. Is the '8-bit equivalent resolution 1bit' different from a regular 1bit dac and why 'combine' it ? I'd imagine a 4-8 bit dac by itself would be good enough ?

[phn]

So for me there is already a relation between measurement and sound.

Here's an example where objectivists and subjectivists agree:

<<Stereophile also performed a large subjective listening test between some existing high performance recording formats and SACD was even considered to be inferior to PCM 16bit, 176,4 kHz.

Anyway, one should not take too much notice of "how many" said this or that. What is important is how things really are, not how many people believe this or that. Deciding truths by voting is seldom a good way. It can only show what people believe. Some peoples beliefs might of course be right, but to often correct information and relevant listening experiences drowns in common misconceptions, preconceived notions and the media background noise.>>

I won't argue about measurements and what you can hear or not hear. (It's also difficult to make a fair comparison between CD and SACD because of the limited frequency range of the former.) But the poor measurements of the SACD evidently do result in poorer sound.

And it's also pretty evident, as I see it, that CD, HDCD and DVD-A are the only audiophile formats out there. Unfortunately HDCD will go nowhere. There's simply no money in it. And DVD-A has so far been targeted exclusively for the surround crowd. Which leaves us with CD as the only real audiophile format.

[ThorstenL]

Konnichiwa,

Originally posted by percy
Ok. So what is the difficulty in implementing a true 16-bit dac ? (the 'how stuff works' link above tried to explain that but it went over the top).

There is no real difficulty, merely high [recision, thermally matched resistors are required and other precision analog circuitry, this simply costs and if you make it all on silicone the rate of chips that do not pass muster is high.

On the other hand 1-Bit type DAC's are purely digital devices, very cheap to make.

Originally posted by percy
I think I understood the part about Multibit DAC's of low resolution (4-8 bit) in the sense that it must be allowing to use a lower (than Ghz) frequency, right ?

Yes, it you operate a DAC with 8 Bit Resolution with a 256 X Sample Rate clock then the combination of pulse width modulation and multibit DAC can be combined to make a DAC with a true 16-Bit equivalent resolution.

Originally posted by percy
But I didn't understand the part about combining it with '8 bit equivalent resolution capable 1-bit'.

What it suggests is that by combining the methodes applied to a 1-Bit DAC with a multibit DAC can achieve higher native resolution than either alone.

Originally posted by percy
Is the '8-bit equivalent resolution 1bit' different from a regular 1bit dac and why 'combine' it ? I'd imagine a 4-8 bit dac by itself would be good enough ?

A DAC with 4-Bit or 8-Bit resolution would be very poor sounding. A 1 Bit DAC with 256 X Sample rate clock is, without applying a lot of trickery to it in effect also merely an 8-Bit DAC.

If you want, windows audio works with 8Bit wav files, just get cooledit and change a Music Filke to 8-Bit and listen.

So, if I now use the 1-Bit part for the lower 8-Bit in audio and the Multibit part for the upper 8-Bit you have a 16-Bit capable device combining the two.

Sayonara