Pitch (Frequency): heard in Octaves
                        Sound “Do” in musical scales:
                                      C1. 32.703  Hz.
                                      C2. 65.406.
                                      C3. 130.81.
                                      C4. 261.63.  (middle C)
                                      C5. 523.25.
                                      C6. 1046.5.
                                      C7. 2093.
• Two-tone discrimination: like two-point discrimination in the
somatosensory system. Proportional to the frequency (~ 5%).
• Weber-Fechner Law
• WHY? Physiology: “place” map for frequency coding from the
cochlea up to cortex; sizes of receptive fields. Just like
somatosensory system