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1bit 2bit 3bit 4...

post #1 of 8
Thread Starter 
I've been looking around a different audio players, portable and decks, and they all like to state what type of digital-analog coverter they have.
Trouble is, I have no idea what exactly is the difference between a 1bit DAC, 16bit DAC, 24bit DAC, hybrid pulse DAC, 24bit current pulse DAC, etc, etc.

What is the better DAC to have in portable gear (my PCDP boasts a 1bit DAC, as do both my MD units) and decks (some brag 24bit, others 16bit), and what exactly is the difference?
post #2 of 8
It's the algorithm that is used to make the Digital to Analogue conversion.

Obviously, a 16 bit DAC is more advanced that a 1 bit DAC. Probably differences in transparency sonically speaking.
post #3 of 8
I beg to differ here. I looked deeply into the matter when all the talk about upsampling and oversampling was going on and among other things I read I found in the literature that 16-bit DACs are not necessarily superior to 1-bit ones, in fact may be inferior.

From http://members.chello.nl/~m.heijlige...tml/dactop.htm :
Multibit feedback noise shaping
The modulator properly predistorts (noise-shapes) the oversampled digital signal sent to a lower-resolution multibit DAC so that when properly analog-postfiltered its output will yield the full 16-bit resolution stored on the CD. This is the oldest scheme common in consumer products, widely popularized by the NV Philips SAA 7030 / TDA 1540 chip set (1983) with a 14-bit internal DAC and 4:1 oversampling yielding 16-bit final resolution.

Under ideal circumstances, a 16-bit converter would exactly convert all 16-bits of the sample data word in a linear fashion. Inaccuracy in the most significant bit (MSB) of the data word can result in an error of half the signal's amplitude. Multibit convertors are also plagued by gain error, slew-rate distortion, and zero-crossing distortion. All of these error and distortion types introduce severe harmonic distortion and group delay; thereby perturbing signal stability, imaging, and staging.


Comparison of different conversion methods
Each of these competing modulator topologies has technical strengths and weaknesses that are very involved and do not lend themselves to summary. The signal fidelity in each of them can be excellent but depends on different sets of circuit elements. It is all a matter of "second-order" electrical effects; if the components are all perfect (as they invariably are assumed to be, in popular explanations of this subject matter), then all the techniques work equally well. Audible differences are much more likely due to other design choices inside the DA convertor, like the quality of analog-digital ground isolation, or the choice of output-filter op amps etc.

Measurements of THD and linearity error for various 16-, 18-, 20-, and 1-bit converters yield interesting results. PWM and PDM converters (note: '1-bit' DACs) show < ¡Ó 1 dB linearity for input signals from -100 to -80 dB and are virtually linear thereafter. Some of the most expensive players on the market with 18- and 20-bit converters using 4-, 8-, 16-, and even 32-times oversampling yield up to ¡Ó 4 dB linearity error for signals as high as -75 dB. In the THD tests performed with a -60 dB 1 kHz sine wave test signal, the expensive multi-bit players showed harmonics up to the 13th at levels greater that -110 dB. Only the PDM converter was able to hold all non-fundamental harmonics under -110 dB.
(No, I didn't understand half of it either ) but I think you can see that it is far from clear that 16-bit or even 18- and 20-bit converters are superior to 1-bit converters.
post #4 of 8
Mystyler: As far as I understand matters, the basic difference between a mutli-bit- and a single-bit-dac is that the multi-bit-dac is designed to directly convert the data-words from the cd to corresponding analog voltages, whereas the single-bit-dac needs to fill a buffer (capacitor) with a certain amount of tiny current pulses in order to build up the corresponding voltages. Thus a higher clock rate for the single-bit-dac is needed. Nevertheless, the quality of the output seems to have more to do with proper implematation of the dac, less the principle of the dac - so you can't generally claim that a multi-bit-dac will sound better than a single-bit-dac or vice versa.

Greetings from Munich!

Manfred / lini
post #5 of 8
Thread Starter 
Ok then, so it doesn't really matter how many bits the DAC is, just whether or not its an El-Cheapo $2 job or something of more quality?
post #6 of 8
It seems that 1 bit DACs are easier to make work properly and well on the cheap...
post #7 of 8
Joe is quite correct. 1 bit is easier to make and is cheaper. If all DACs are perfect, there will be no difference. The cost is really in the testing of the DAC (quality of the accuracy). The biggest error came from the MSB transition.

Let's assume a 4 bit resolution. At half scale (i.e. MSB), the word is 1000 and at 1 LSB less the word is 0111. With multi bit DAC design, the weight of each bit is cumulated. Assume each bit has 0.05V error, then the 0111 word will have 0.15V error vs 1000 have only 0.05. The quality of transition from 0111 to 1000 obviously is not very good.

My point is don't worry about the technology but pay more attention to the quality of the manufacturer. If manufacturer A has 50% (that's not a real world number), then you have only a 50% chance to get a quality product. With quality manufacturing, (let's assume 99.99%), then you'll have to be very unlucky to get a lemon.
post #8 of 8
Thread Starter 
So I should steer clear of el cheapo brand then.

Now, I'm thinking of a Minidisc deck, either the 470 or 940. Would there be much improvent in sound quality in the 940 over the 470?
They both use different DACs, so I assume there would be...
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