For example, with FM radio, the strength of the 100 MHz carrier with modulations would be considered for CNR, whereas the audio frequency analogue message signal would be for SNR; in each case, compared to the apparent noise.
In fact, the information (bits or symbols) is carried by given combinations of phase and/or amplitude of the I and Q components.
High C/N ratios provide good quality of reception, for example low bit error rate (BER) of a digital message signal, or high SNR of an analog message signal.
are the root mean square (RMS) voltage levels of the carrier signal and noise respectively.
When considering only the receiver as a source of noise, it is called carrier-to-receiver-noise-density ratio.
When expressed in logarithmic scale, the reference value for decibels, 1 Hz, is often denoted "dB-Hz".