The correct answer is: S1 and S2 are true.
Fidelity is a measure of how closely a reproduced signal resembles the original signal. It is often used to describe the quality of audio or video recordings. Fidelity is typically measured in terms of signal-to-noise ratio (SNR), which is a measure of the ratio of the power of the desired signal to the power of the noise. A higher SNR indicates a higher fidelity.
Fidelity is also affected by the reproduction of phase relation. Phase is the relative timing of two signals. If the phase of a reproduced signal is not the same as the phase of the original signal, then the reproduced signal will sound different. For example, if the phase of a reproduced audio signal is shifted by 180 degrees, then the sound will be inverted.
Therefore, both S1 and S2 are true. Fidelity represents the reproduction of both the signal and the phase relation.