I would like to know what is the most efficient way to design and ADC input for professional and consumer levels (without using any transformers). I have a codec that accepts a 1 volt rms input, so the input signal can swing between 2.8 volts p-p. That signal can be handled properly with 5 volts for power supply in the opamps, so I am wondering why most equipment still have +/-18 volts in their opamp's power suplly rails. It is for headroom? After all, the codecs will have external protection diodes to Vcc and Vss to clamp the input no more than their Vcc and no less than their Vss levels (+3.3 V and ground) Thank you for any information.