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I am using Librosa to detect pitch in a guitar audio signal. I have very little background in signal processing, and I was quite confused with the distinction between analog - digital signals and continuous-time - discrete-time signals.

I am aware that, when I load an audio file in Librosa like this:

y, sr = librosa.load(filename, sr=11025)

I convert the signal to discrete-time. I think that's true as otherwise I wouldn't need to provide an sr.

However, is the signal digital or analog? I see that the analog signal is defined as:

A signal whose amplitude can take on any value in a continuous range

So when does the conversion from analog to digital happen? Or am I working with analog signals?

pavlos163
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    See https://dsp.stackexchange.com/questions/19830/analog-signal-can-be-discrete-time and many other related questions on this site. – MBaz May 22 '17 at 19:25
  • I understand the difference between those. However, the signal with which I am working, is it digital or analog? Is it quantized when I call load or when it is recorded with a microphone? – pavlos163 May 22 '17 at 20:08

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A microphone just converts pressure to voltage. Still analog. Everything that you do inside a computer is digital. So, quite frankly obviously, the digitization happens between microphone and software: that's what the soundcard does. Whatever you do with DSP is, by definition, digital...

Just because your software needs info about the sampling rate by no means implies the signal is still analog; that's an absolute fallacy. A digital signal is just a sequence of numbers; there's no sampling rate info inherent to such a sequence.

Marcus Müller
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  • I see, thanks. "Just because your software needs info about the sampling rate by no means implies the signal is still analog" -> does it imply that the signal is still continuous-time? Or is that also wrong? – pavlos163 May 23 '17 at 11:47
  • yes, also wrong. As said, it implies nothing. – Marcus Müller May 23 '17 at 12:38