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Basic technical question about digital source signals

Forgive if this is a stupid question, but the current thread about digital vs analog made me curious: if you look at an analog music signal you see (I think) summations of sine waves i.e. a signal waveform which is "smooth". I realize that there are many contributions to digital sound, but starting with the most basic, if you look at the output from a digital source e.g. on an oscilloscope, would it appear "smooth" i.e. has all the stairstepping that occurs when you convert digital to analog been smoothed out or would the signal appear jagged to some extent?

Thanks for your time.
berner99
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cleeds
5,702 posts
 
berner99
... if you look at the output from a digital source e.g. on an oscilloscope, would it appear "smooth" i.e. has all the stairstepping that occurs when you convert digital to analog been smoothed out or would the signal appear jagged to some extent?
The "stairstepping" you refer to is really a misnomer, although it's widely believed. For proof, see this.
audio2design
1,351 posts
 
Cleeds,

In that video, he is showing the output of a DAC with an analog reconstruction filter. It is filtering out the stair-steps. Which goes back to my post, on most DACs, there would be no stair-step evident. On non oversampling DACs or any DAC without an analog filter, there would be evidence of stair-steps.
gs5556
1,218 posts
 
You will see an analog waveform. There is no such thing as a digital stair step waveform because a digital signal does not have a defined value between two points in time. It has only one discrete point, and that point in time is the instantaneous sample point. The "starstep" draws a line between two sample points, or it draws a line where the signal does not exist. It is just a picture created on paper to visualize a digital signal.


audio2design
1,351 posts
 
The output of a DAC sans built in filter or external filter will be a stairstep. I can't think of a DAC in audio that is not convert and hold.


gs5556, that is a conceptual answer, not the reality of an actual DAC. Not many (any) DAC have an impulse function output.
jjss49's avatar
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jjss49
6,612 posts
 
google "digital to analog conversion' and 'nyquist theorem'
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