# Data taken from 
# L. B. Evans and H. E. Bass, 
#    “Tables of absorption and velocity of sound in still air at 68F (20°C),” 
#     Technical Report No. AD0738576,
#     WYLE LABS HUNTSVILLE AL HUNTSVILLE United States
#     Report Date: 1972-01-01 
# 
# https://apps.dtic.mil/sti/citations/AD0738576
# https://apps.dtic.mil/sti/pdfs/AD0738576.pdf
#
# Freq_Hz    Vel_(1000_ft/s)     (Vel-Vel400)/Vel400
       20     1.1268920             -0.0002457 
       40     1.1270130             -0.0001384 
       80     1.1271120             -0.0000506 
      160     1.1271540             -0.0000133 
      200     1.1271610             -0.0000071 
      400     1.1271690              0.0000000 
      800     1.1271720              0.0000027 
     1600     1.1271720              0.0000027 
     2500     1.1271740              0.0000044 
     5000     1.1271800              0.0000098 
     8000     1.1271830              0.0000124 
    12500     1.1271860              0.0000151 
    20000     1.1271870              0.0000160 
    40000     1.1271880              0.0000169 
    80000     1.1271880              0.0000169