Is no DAC the best DAC?

September 21, 2017
 by Paul McGowan

I’ve been answering a lot of great customer questions on Ask Paul. One of them was a simple misunderstanding, but it sparks good dialog.

On the DIY forums, a poster suggested he was converting digital audio to analog without the benefit of a DAC and the question posed to me was, “Is that possible?” The answer should be a simple “no” but then it’s never quite that simple.

Let me first explain what the poster on the DIY site was doing: converting DSD to analog with little more than an output transformer. Thus, he didn’t need a “DAC” to make music, he needed only a single part.

DSD is very different than traditional PCM. If you were to try the same technique of decoding PCM with a simple capacitor, you’d get nothing but noise (if you got anything at all). This is because PCM isn’t anything close to analog, while DSD is as close to analog as any digital format can be. Look at PCM on a scope and you see nothing recognizable as music (it’s a code, after all). Try the same thing with DSD and you can actually see the music.

This difference is one reason why our digital guru, Ted Smith, converts everything to DSD in our DirectStream and DirectStream Junior. Their output stages are essentially simple low-pass filters (like the transformer I mentioned earlier). DSD is already close to analog and requires very little post-processing.

In direct answer to the reader’s question whether it’s possible to play digital music without benefit of a DAC, I would answer, no. Anything used to convert digital to analog is, by definition, a DAC.

This is a subject I go into in some detail in this video.

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15 comments on “Is no DAC the best DAC?”

  1. The word ‘digital’ is normally used to describe a technology in which sequences of binary digits (bits, 0 or 1) are used to represent other quantities, typically numbers or characters. it is the patterns of 0’s and 1’s which carry the information. PCM is an example of this. 16/44.1 means that the analogue signal level is sampled 44,100 times a second and represented as a 16 bit number. The instantaneous level is represented as a pattern of bits.

    PDM (pulse density modulation) is rather different. Here, although the pulses look like digital bits, with a fixed level and width, no encoding is taking place. Instead each pulse is a fixed unit of charge, and their frequency averages out to a current which is the analogue signal.

    DSD (direct stream digital) is PDM with a defined maximum pulse frequency. It is not a digital stream as we normally use the word. I think today’s topic is really about the use of the word digital, or rather its misleading use in the term DSD. A conventional DAC cannot handle DSD because DSD is not really a digital format. You do not need a DAC for DSD, just a low-pass filter.

  2. I know it is oversimplification, but I cannot resist. It appears on the surface that we are going somewhat fuul circle and using transformers in the signal path once again, like vacuum tube equipment.

    It just struck my funnybone this morning. Great subject for discussion, once again.

    Jack

  3. While it’s true that anything that converts a DSD stream to analog is a DAC, it is certainly possible to convert a DSD stream to analog without a chip. I am currently using a Denafrips Pontus R2R Dac that uses a proprietary 6-bit resistor network to do that.
    Denafrips’ bigger Dac, the Terminator, has just been awarded a Blue Moon award on 6Moons.
    All Denafrips Dacs convert D to A with a R2R resistor network, certainly not the newest technology, but apparently a good sounding one. No Sabre, no CS, no AK, no chip at all.

    Stefano

      1. I was lucky to find the way to the DS/Bridge without any wrong paths inbetween, right after a โ€žnormalโ€œ 12k CD player I even could sell well at the time.

        It was a step up in multiple ways. Hires streamng without needing a separate outboard source for the DAC, state of the art timing, ambiance, imaging and openness/extension and software upgradable plus reasonable price.

        Any resistor network doing the same highly welcome ๐Ÿ˜‰

  4. It is interesting to observe that only with a 1-bit format can a digital bitstream ever be identical to the analog data it represents, hence the party trick with the transformer.

    1. As far as I heard, DAC chips change their behaviour according to temperature. Should not a R2R DAC be even more dependent on temperatur changes – and ageing resistors?
      Second question: Is a 6 bit DAC the same as a 1 bit DAC?

      1. R2R DACs are so dependent on parts matching and temperature that it’s a miracle they even work as well as they do. And yes, they change with temperature.

        A 3-bit (or even a 6 bit) can mean the use of multiple sigma-delta 1-bit modulators and the outputs are averaged for better consistency.

  5. R2R Ladder, Sig-Delta, FPGA based DACs can and do sound very very good, the devil is in the detail of the implementation along with the necessary filters, clock(s), boards, layout, isolation etc.
    I wouldn’t throw out an MSB DAC or some of the other make just because they are not FPGA based.
    Digital has its own “tribes” and they are growing. Goodness there will as many to rival the big black disc aficionados soon.

  6. The best way to view and categorize DAC architectures is to break them down into the three basic functions that they must all provide:
    1. Pre-processing of the incoming digital signal
    2. Actual conversion of the digital signal to analog
    3. Analog output stage (including any and all required filtering)
    Ultimately, all DACs can be classified according to how they perform those three functions … and in particular the first two functions.

    But as someone who has pored over, observed, and listened to, many of the thornier aspects of digital audio for the past 5+ years, I have concluded that the one thing most likely to determine the sound quality of a DAC is the quality of its analog output stage. And not by a small margin.

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