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Interpreting Ear Witness Testimony - Herbert Blenner - 25-02-2015 An unobvious characteristic of hearing caused many ear witnesses in Dealey Plaza to perceive echoes instead of the direct sounds of gunfire. Suppose a shooter fired a rifle from TSBD. Two sounds from the muzzle blast would reach an ear witness in Dealey Plaza. The direct sound would arrive tenths of a second before echoes from the County Courts and County Records buildings. Instruments at the location of this witness would measure a higher power for the direct sound and substantially longer duration for the echoes. Geometry of this situation stretches the duration of echoes by a factor of one hundred and reflection of sound diminishes power by a smaller factor, hence the energy of the echoes impinging upon the ears of a witness would exceed the energy from the direct muzzle blast. From these considerations alone we can understand why some ear witnesses heard the sounds of guns shots coming from either Country Courts or Country Records. These witnesses perceived the stretched reflections of far briefer muzzle blasts, which originated elsewhere. Our ears attenuate brief sounds. Wave files containing sounds with constant and variable durations demonstrate this effect. All sounds have the same power and differ only in their durations. The sounds with selectable durations, being centered around 0.5 and 2.5 second, surround the constant duration sound that begins at 1.0 second and ends at 2.0 second. Users of Sound Recorder can drag their slider to the indicated times and observe the widths and amplitudes of these sounds. When the duration of sounds are one hundred milliseconds, we begin to notice the decrease in perceived loudness. http://hdblenner.com/earwitness_files/TwoHundredMs.wav http://hdblenner.com/earwitness_files/HundredMs.wav The attenuation increases slowly until the duration of the sounds becomes tens of milliseconds. http://hdblenner.com/earwitness_files/FiftyMs.wav http://hdblenner.com/earwitness_files/TwentyMs.wav http://hdblenner.com/earwitness_files/TenMs.wav Further decrease in the duration, rapidly increases attenuation. As durations approach one millisecond our ears perceive a few percent of the loudness of fixed duration sound. http://hdblenner.com/earwitness_files/FiveMs.wav http://hdblenner.com/earwitness_files/TwoMs.wav http://hdblenner.com/earwitness_files/OneMs.wav Hearing relies upon physical mechanisms to convert sound waves to neurological signals. As a result our perception of sound inherits the response characteristics of the mechanisms. In particular our ears ignore the power or amplitude of brief sounds and respond to the contained energy. A wave file containing pulses of equal energies, decreasing amplitudes and increasing durations shows this effect when durations are briefer than tens of milliseconds. http://hdblenner.com/earwitness_files/isoenergetic.wav