In most sound card designs I've seen there is a 'boost' switch on the output. In other words there is a toggle that enables a ~10dB boost on the output amplifi

In most sound card designs I've seen there is a 'boost' switch on the output. In other words there is a toggle that enables a ~10dB boost on the output amplifier (or sometimes the DAC). The volume control is actually digital but when you hit a particular threshold the external boost is toggled on and digital volume adjusted to maintain a smooth level transition. If you keep going 'up' with the volume control your still changing the volume digital but you've now got an extra 10dB of gain on the output which can drive the output into clipping if the input signal is full range. EDIT: Just to add. I would be extremely surprised to see a sound card that isn't a full on pro model have true analog gain control. I've designed a couple products with such controls (for pre-amp gain, but a similar concept) and you need digitally controlled resistors to accomplish it. They are large, expensive and touchy to route without inducing noise. As an example: http://www.analog.com/en/digital-to-analog-converters/digital-potentiometers/ad5246/products/product.html http://www.analog.com/en/digital-to-analog-converters/digita...