IT has been observed, when using short pulses of tone for echo-location in auditoria, that pulses which are too short to give any clear impression of pitch when heard directly from a loudspeaker seem to assume a more definite pitch when radiated into an auditorium. One of us mentioned this point at a recent meeting of the Acoustics Group of the Physical Society, and, as several contributors to the discussion questioned the effect, it is thought that this account of controlled tests will be of interest.