Week 3- the human ear

The Outer Ear
The outside of the ear, the pinna and the ear canal act as a tunnel, making the vibrations of a sound wave travel to the ear drum which in turn vibrates. this vibration amplifies the sound so that we can process the sound. the pinna also allows us to percieve the direction of the sound source. 

The Middle Ear
The vibration of the eardrum is transferred through the chain of small bones, the ossicles, which then vibrates the oval window of the cochlea.  this chain helps to make up for the lost energy when the vibrations travel through air. this then goes through the fluid in the cochlea.

The Inner Ear
Vibration of the oval window produces pressure waves in the cochlear fluid that stimulate the cochlea. Sensor cells within the cochlea cause neurons connected to our brains percieve this. They transmit timing, amplitude and frequency information to the hearing part of our brain.

Human Hearing and Speech
Human hearing covers a range of frequencies from around 20 Hz to 20 kHz and responds to a huge range of sound levels.

in this range are frequencies and levels generated by speech.
The lowest sound pressure level (SPL) that humans can hear varies with frequency and is called the Hearing Threshold.
the best sensitivity is normally in the frequency range of 1 kHz to 4 kHz.

MPEG/MP3 Audio Coding
The use of MP3 of a lossy compression algorithm is designed to reduce the amount of data required to represent the audio recording and still sound like the original soundtrack. A MP3 file that is created using 128 kbit/s will result in a file that is 11 times smaller than the CD file created from the original audio. A MP3 file can also be constructed at higher or lower bit rates, with higher or lower resulting in a difference in quality.
The compression works by reducing accuracy of waves that are considered to be beyond the hearing ability of most people. This method is referred to as 'perceptual coding'.