If a narrow bandpass filter is driven by a periodic train of narrow rectangular pulses, the resultant wave train elicits a strong pitch perception which varies monotonically with the pulse repetition rate. This periodic wave train can be used as a pitch reference to match against various stimuli. Consideration of double wave train stimuli with various delays establishes sharp dichotomy between the perception of pitch and timbre. Further evidence is adduced in support of the development of a partial model of psychoacoustic perception which is plausible in terms of the known physiologic mechanisms. In brief, the total acoustic stimulus undergoes a differential filtering action along the cochlear partition due to the resonant characteristic of the cochlear structure. The response characteristic of any particular segment of the partition exhibits a single broad peak and consequently has a relatively fast time response. The envelope of the response is assumed to be detected by a relaxation detector having a relatively wide dynamic range, and periodicity of the envelope is detected by a delay-line detector. The second-order time envelope of the cochlear-partition response defines a function over the length of the partition. The shape of the envelope (along the partition) of the absolute value of this function elicits the perception of the timbre structure of the total stimulus. The total area under this envelope elicits the perception of the loudness of the total stimulus. This combination of broad-band spectral filtering, envelope detection, and delay-line periodicity detection provides both a mechanism for relatively sensitive pitch discrimination and for spectral discrimination with relatively fast time response.