I am learning about digital filters and came across the link Why do digital filters work?
In real world communications, I think the input to the channel is in analog after being modulated by digital modulation techniques such as BPSK, Qam etc. These modulation techniques convert the real valued signal to a symbol space. The following questions may seem trivial and can be found in text books, but it is difficult to extract specific information.
I am unable to understand, is the input to the channel real valued numbers or symbols?
Is the modulated signal passed into the channel? IS the modulated signal digital?
If not, Why should we do digital modulation if the signal entering the channel is analog and in which stage do we need digital filters?
An example with a block diagram would be helpful. Thank you