What is noisy signal?

[naseeam]

In general, what does phrase noisy signal mean? Let's say some sensor puts out 0-5V square wave with a frequency to 50KHz, what would it mean when someone says it's a noisy signal. Sometimes, when people look at this signal in oscilloscope, they say it's a noisy signal. What is noise? How do they know it's a noisy signal? Where is noise coming from?

 

[dknguyen]

Noisy means that the waveform has random high frequency components in the signal, along with the frequency components that are supposed to be there. It comes from many things like electrons vibrating randomly (due to heat), as well as ambient electromagnetic pulses, and lots of other stuff that isn't perfect.

In your example, it would mean that instead of a perfect DC voltage when the square wave is in between transitions, it would jitter randomly at a high frequency about rather than sit constantly at low or high.

You know what a sine wave looks like right? Suppose that is the signal you are trying to get. Here is what it might look like with noise:
https://www.school-for-champions.com/science/images/noise-60hz.gif

 

[audioguru]

Audio noise is a hissing sound in the background.
Remember old audio cassette players made before Dolby noise reduction??

Video noise is specs all over the picture.
Remember old analog video cassette players made before the digital ones??

 

[Nigel Goodwin]

Remember old analog video cassette players made before the digital ones??

Except there never were any digital VCR's? - at least not in Europe.

 

[TrevorP]

Except there never were any digital VCR's? - at least not in Europe.

Yeah weren't they all Analog? I've never heard of a Digital one.

 

[dknguyen]

Nor I. Who would bother to make digital VHS tapes?

 

[audioguru]

My digital TV recorder/player had a hard drive for recording and playing back both at the same time! It costted too much so I returned it and now I use my VCR again for recording and playing back.

My digital cable TV has stations all across North America in 3 time zones. So if I forget to watch a show or if I forget to record it then I can see it 1 hour, 2 hours and 3 hours later from the distant cities in each time zone.
COOL!