Sound coding is for FREQUENCY and LOUDNESS

Spatial coding maps Frequency (pitch). The location along the cochlear duct is activated as the frequency place on the basilar membrane. Nerve connections are responsible to carrying the frequency signal from the spiral cochlea to connections on CNS neurons. The frequency map remains throughout the auditory pathway and into the cerebral cortex.
Nerve Firing Frequency maps Loudness (intensity coding).
Firing frequency of nerves is limited between 0-1000 Hz. This restricts the resolution of intensity so that, in addition, the number of fibers firing codes for loudness. For example, inner hair cells have up to 40 single CNS projecting afferent axons making synapses on their base.