shakeshuck wrote:I thought that 1 bit per sample meant the value of the wave would increase 1 step up the 'ladder' per sample of bitrate

That is almost what PCM does.

For simplicity, if we imagine 3 bit unsigned audio data, and we think of the analogue output as "voltage" (which ultimately it is), then 000 represents the lowest voltage, and 111 represents the highest voltage. The 'ladder' is: 000, 001, 010, 011, 100, 101, 110, 111, and we could say that an increase of "one" (that's an increase of 001) represents one step of the ladder. In this example, where we have 3-bit samples, the 'ladder' has 8 rungs. However, when converting from digital data to analogue, we don't actually increase the voltage in steps. The rate at which the voltage rises from one level to the next is limited by a low pass 'reconstruction' filter so that the rate of change is never more than half the sample rate.

For DSD, and leaving aside "wide DSD", we don't have "samples" in the conventional sense, we just have a stream of 0s and 1s. When a 1 is encountered by the DAC, the output voltage rises, and conversely when a 0 is encountered, the output voltage falls. As with converting PCM to analogue, the rate of change is limited by a low pass filter. A "1" in the stream tells the DAC to increase the output voltage, but not by how much. If the next, and the next, and the next bits are all ones, then the output voltage will continue to rise up to the upper "rail" voltage, and the rate of change is governed by the filter.

Another way of looking at DSD is in purely mechanical terms. If we have a

'black box' with a DSD input at one end and a speaker cone at the other, then each "1" represents a little push on the speaker cone, and a "0" is "not a push". The low pass filter removes the jerkiness of individual pushes so that the speaker moves smoothly at frequencies within the audio range.