DAC attack

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Yesterday we detailed the layout of a PCM DAC and its 4 components that make it work: the input receiver, DAC itself, Current to Voltage converter and finally the analog stage: the subject of this series. We want to try and understand why the output analog stage plays such an important role in the way a DAC sounds - which may run a bit counterintuitive because 1/2 the DAC components are digital - the other half analog, yet they are definitely not equally weighted when it comes to how good a DAC sounds. We also reviewed the 1st of the 4 components in the DAC, the input receiver, and learned that one way or the other, we need to make sure our digital audio data has been converted to I2S - the native format for digital audio within the DAC. I2S has 3 separate clocks and a data line. Now we have the I2S data in the form we want and we're ready to let the 2nd component in the DAC chain work its magic. We have covered the DAC itself in several series, starting as far back as November 9th. You can go back in the series here if you wish and catch up to us or just hang in there till we get to the meat of this series. We know that most modern DACS are 24 bit and to achieve this level of resolution they are actually not traditional ladder DACS, but rather single bit DACS (sometimes 2 or 3 bits) similar to how DSD is handled. Here's what's important to grasp in this phase of our understanding: once the data has been organized the way we want it is sent through the DAC and processed through upsamplers, digital filters, sigma delta converters and all sorts of crazy modules few of us will ever understand or need to. What comes out of this mess is a conversion of what we started with - numbers representing voltage levels - into 24 current steps. Each step is twice the current as the next and between them we have managed to almost get back to where we started when we encoded the music in the first place. Tomorrow we will magically change these current steps into voltage steps - exactly where we started - and then get to work on turning it into music once again.
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Paul McGowan

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