Apparently decibels don't figure into it.
After consulting Martin A. Uman's basic reference book on lightning, I summarize the following:
From measurement of the time of arrival of the first sound of thunder we can determine the distance to the closest point of the lightning channel.
From the thunder's duration we can determine a minimum length for the channel.
Generally the pitch of thunder is 50 cycles per second. From measurement of pitch and use of appropriate theory, scientists have determined the energy input per unit length of lightning stroke channel (100,000 to 1,000,000 watt-seconds per yard of channel length).
Thunder pitch is also influenced by air density and altitude.
