Method 597 velocity and
c is the speed of sound. Typical bullet velocities and their shock-
wave angles are 680m
/ s (giving a cone angle of 30
◦ ) up to about 850m
/ s (giving
a shockwave angle of 25
◦ . When the bullet moves at exactly the speed of sound
c =
V = 340m
/ s the shockwave is at 90
◦ and so moves in the same direction as
the bullet. To the side of the weapon there is a mixture of sounds, with their
relative times depending on angle and distance.
Even in an open field one echo is always found: the ground reflection of the
muzzle signature and bullet flight sound. We also expect to hear ambient reflec-
tions from nearby buildings, trees, and then late echos from distant objects.
Large mounted guns coupled to the ground can send shockwaves through the
earth at up to five times the speed of sound in air, so these may arrive ahead of
the projectile on dense (granite) terrain, giving artillery targets a brief warning.
Let’s summarise the contributory sounds and factors shaping the sound:
• Detonation impulse (munition signature)
• Gassing (muzzle signature)
• Body ring (weapon furniture signature)
• Automatic recycling (mechanical signature)
• Bullet flight (supersonic crack, Mach signature)
• Early reflections (bullet flight and muzzle ground reflection)
• Ambiance (trees, buildings)
• Observer position (shooter, downrange or side)
• Subterranean propagation, from heavy weapons
Model Our model will comprise several separate components, each producing a short
sound that can be mixed to provide a superposition appropriate to an observa-
tion point. Each component has a delay to offset it against the others. A filter
bank creates the modal character of the weapon body. This can also be used
for handling noises such as reload, chambering bolt and magazine slides when
excited by a suitable friction pattern.
Method The detonation is provided by a chirp impulse. We are not able to produce a
suitably energetic impulse in the short time of a few microseconds using digital
synthesis since only a few samples would be available. A critically short (about
10ms) sine sweep produces the correct effect. Muzzle blast is a much lower
frequency, but again we will use a short sweep around 100Hz to obtain the
required density. The weapon body is simulated with a set of series band-pass
filters and excitation of the weapon will be a short noise burst. The N-wave
shock signature is produced directly by a
object with a delayed and low-
pass filtered version accounting for ground reflection. Some distortion using a
or table transfer gives more high-frequency energy to the sound in order
to brighten it up.