Audio DACs are actually a lot more complicated than you might think. Human hearing is very sensitive to non-linearity and noise, especially certain kinds of noise. In terms of raw performance, the linearity and noise requirements were definitely the most demanding as far as state of the art when I was doing research. They're certainly still tougher than anything in the RF space (specifically cellular, bluetooth, and wlan). Also, because most of them use delta-sigma modulators, the jitter requirement was also very stringent, though high-performance digital and RF may at this point need lower jitter than audio.
Unfortunately a lot of the advancement, especially in the high end space, is proprietary. I read a somewhat vague article about some of the more recent innovations, and one that stood out was the need to set the Initial Condition of the Delta Sigma Modulator in a specific way. Delta Sigma quantization noise is notoriously poorly behaved, and because of its periodicity, it was actually perceptible even at its lower levels.
I would agree that audio DACs are indeed a "solved" problem, but at this point so is pretty much everything in integrated circuit design. Most advances in design are very incremental. The need for innovation comes from the continued push to reduce power and cost. Eventually you have to change process node - smaller transistors means a smaller die and lower cost, and also lower power for many circuits. That tends to be very challenging for a lot of mixed-signal circuits because the smaller transistors are worse in analog domains. You end up having to play a lot of tricks to make things work, but its pretty well understood and nothing revolutionary.
Unfortunately a lot of the advancement, especially in the high end space, is proprietary. I read a somewhat vague article about some of the more recent innovations, and one that stood out was the need to set the Initial Condition of the Delta Sigma Modulator in a specific way. Delta Sigma quantization noise is notoriously poorly behaved, and because of its periodicity, it was actually perceptible even at its lower levels.
I would agree that audio DACs are indeed a "solved" problem, but at this point so is pretty much everything in integrated circuit design. Most advances in design are very incremental. The need for innovation comes from the continued push to reduce power and cost. Eventually you have to change process node - smaller transistors means a smaller die and lower cost, and also lower power for many circuits. That tends to be very challenging for a lot of mixed-signal circuits because the smaller transistors are worse in analog domains. You end up having to play a lot of tricks to make things work, but its pretty well understood and nothing revolutionary.