Hi, I wonder if someone could shed light on my question. It's kind of related to Fourier Transform and attenuations on signals. As everyone knows, in the early days, the communication on the local loop was on dial up which was basically analog communication.The digital data in computer gets modulated to analog signal and transferred over the phone line. You often see the reason of this as the phone line doesn't have enough bandwidth to pass the digital signals which contains very high frequency components that could be easily attenuated. I understand that for the high bit rate communications, but I don't see the reason why this fact restricts the communication at the lower bit rate.. The max bit rate on dial-up is 56kbps, but couldn't we do the same bit rate without modulation ? Let's say serial communication at 56kbps in digital form. The worst case is the data toggles every cycle at 56kHz, and this contains very high frequency components which are prone to the attenuation, however, we actually don't need all the ultra high frequencies. The phone line might be able to pass the first few harmonics (starting at 56kHz sine wave or less, depending on the data pattern) which are enough to reconstruct the original data at the receiving end. Considering the fact that ADSL can run up to 4MHz, it should be able to accommodate a decent number of harmonics within 4MHz(or even 2MHz) frequency band to get the "digital" communication done on phone line without a serious attenuation, shouldn't it ? Am I misunderstaning something ? Appreciate your opinion.