Speed of sound is variable depending on atmospheric conditions and elevation above sea level. "Crack" usually means your speeding, try slowing it down and tell us how it sounds.
Makes sense. This was 3000'-3500', low humidity, around 70 deg.
There are a couple of different standards at play, one is referenced by your “1125 FPS” number. The other is based on International Atmospheric Standard (IAS). The figure you referenced is predicated on a temperature of 68*F, or 20*C. IAS is based on 59* (15*C), 29.92” atmospheric pressure. That provides a 1116 FPS reference.
While temperature is a practical reference, the measure is strongly influenced by air pressure. Lower atmospheric pressure reduces the threshold. That metric is influenced by temperature, altitude (pressure) and humidity. An extreme comparison is the SoS in water. At about 70* it is 4870 FPS for fresh water.
The difference at your elevation would be small, but there would be a difference.
