The Sound of Movies

You may have seen the film The Artist, if not it's a good movie and the perfect example of how sound took Hollywood by storm and "talkies" became a new normal of the cinema experience. So how is sound recorded?  It's the same concept for digital and analog(film), the difference is in how the information is stored.



All the information comes from The Filmmaker's Handbook. The content is thinned a little to focus only on the basics of analog and digital recoding.

Analog
Film cameras use a double system. That's because film cameras do not record sound. Instead a tape recorders turn sound waves into magnetic energy to be stores on magnetic tape. Storage is the basic difference between digital and analog recording.

The Microphone
captures the sound waves. inside the microphone is the diaphragm which is like the ear drum. It oscillates (moves back and forth) when there are any changes in sound pressure. The movement of the diaphragm generates electricity. The electricity moves through a magnet and sound pressure turns to electric pressure or voltage.

The voltage travels to the mic preamp which amplifies the voltage strength.

Now the sound signal moves into the magnetic recording head which is an "electromagnet" which is in the shape of a C and has a coil around it. The electricity that passes through the head creates a magnetic field. "advancing and receding sound waves become electrical waves"

Magnetic tapes passes through the magnetic field created in the head, by going through the gap ( a narrow opening in the head).  Magnetic tape has two lays the base and oxide (emulsion layer) where sound is stored. The tape has iron particles, each iron particle is a "miniature bar magnet". As the iron particles pass through the head their polarity changes to match that of the magnetic field. The magnetic filed alternate so all along the tape the iron particles have alternating polarity.

Digital 
Digital begins the same way analog does, which is sound being converted into voltage. From there the sound is processed by an analog-to-digital (A/D) converter. The A/D converter process sound by sampling which is repeatedly measuring voltage level. then the measurements are converted to numbers, the conversation of voltage to numbers is called quantizing.



First a refresher on Sound waves

• amplitude is the height of the wave
• frequency is the distance between the crest (highest points) of wave lengths.

Sampling- because frequencies change often, measurements must also be frequent this is a sample rate. Higher frequencies are faster than lower frequency and improve quality by increasing the sample rate. "the sampling rate has to be at least twice the maximum frequency we hope to capture"

Quantizing- this allows for accurate measures of voltage. Digital recordings use a binary system, so voltage is measured in bits. The bits each have several levels for example "a 16-bit system has 65,536 levels". Higher bits means more levels and that equals higher accuracy.

Try watching a favorite movie muted. How long can you stand it?