In traditional pure-analog designs, a switch-resistor network for volume control works best but is very expensive due to the use of many high precision discrete resistors. Next is a high-quality volume pot. You rotate the pot to change resistance, which in turn attenuates volume. A volume pot is non-linear and has balance issues at low volume.
A DAC typically has a mix of analog and digital inputs. Some DACs convert the analog input into digital to utilize the DAC's internal digital volume control and inputs selection, avoiding the use of expensive analog preamp and volume control as described above. The performance degradation of the analog input that has to go through A2D, volume adjustment and then D2A depends on implementation, which is beyond the scope of this discussion. Digital inputs on the other hand should go through the high-end DAC's internal volume control for best performance.
Therefore it make sense to best adjust the volume in the digital domain for digital signals, and use an analog preamp and volume control for analog inputs.
Our DAC-9 and DAC-10* have analog inputs without A-to-D conversion. We use a mixed analog and digital volume-control design. The digital volume control’s 0.5db steps are sent to the DAC for the best possible result. The DAC’s analog output and analog inputs from other sources then go through a switch-resistor network. The DAC's output is switched straight through with minimum resistance. For analog inputs, the switch resistor network provides the best possible result.
In conclusion, we feel we’ve developed the best type of volume control and preamp for a modern DAC.