Square waves or 1's and 0's?

Square wave is a generic term for a non-continuously changing voltage signal. It changes in discrete steps. It does not necessarily mean a repetitive signal or actually square. IF it were repetitive, then it is a digital oscillation, also known as a clock. Because even clocks have non-50% duty cycles, even clocks are not actually "square".

1's and 0's are defined as: the high state of the signal is "1" and the low state of the signal is "0". the high and low can be defined as any voltage depending on the logic family and physical interface.

All digital voltage signals actually contain analog components since they do not switch in zero time from 0-1 or 1-0, and because drivers and transmission-lines are not perfect, there is also resulting overshoot, ringing etc..

Steve N.
Empirical Audio

Almarg - with S/PDIF the transport level is still 1's and 0's, but the protocol of the interface requires encoding the data to limit the number of consecutive 1's or zeroes, allowing a clock to be recovered as well as the data.

Steve N.
Empirical Audio

Jitter on a digital streaming interface is another thing entirely. This is the time variation of the switching transitions, not just 1's and 0's. The digital feed to a D/A is sensitive to this because precise timing matters. It is also important that the A/D used when recording has low jitter. These two add to make more frequency modulation distortion at the D/A.

See more info here:

http://www.positive-feedback.com/Issue43/jitter.htm

Steve N.
Empirical Audio