Penn State University - School of Visual Arts
Professor: Eduardo Navas (
206 Arts Cottage

Sound General

What is sound:

All sounds are variations traveling through the air as sound waves. Sound waves are caused by the vibrations of objects and radiate outward from their source in all directions. A vibrating object compresses the surrounding air molecules (squeezing them closer together) and then rarefies them (pulling them farther apart). Although the fluctuations in air pressure travel outward from the object, the air molecules themselves stay in the same average position. As sound travels, it reflects off objects in its path, creating further disturbances in the surrounding air. When these changes in air pressure vibrate your eardrum, nerve signals are sent to your brain an are interpreted as sound.

From "Audio Fundamentals" Final Cut User Manual Volume III, 17.

Sound Waves

The Sound wave consists of three elements: frequency, amplitude and phase.

Frequency: the rate or number of times per second that a sound cycles from opposite to negative to positive again. Measured in cycles of Hertz (Hz). Human range: 20Hz to 20,000 Hz. Other frequencies exist, but are not audible by humans.

Amplitude: also known as intensity is the strength of sound waves. Humans interpret it as volume, or loudness.

Phase: the comparison of the timing of two sound waves. Periodic sound waves begin at the same time.
Measured from 0 to 360.
0 = exactly in sync
180 = exactly opposite
Phase cancelation happens when two sounds out of sync are added together.

Spectrum of Sound

Low Frequency = Bass (below 250 Hz)
Mid Frequency = midrange 250 - 4000 Hz (humans hear best)
High Frequency = Treble (beyond 4000 to 20,000 Hz)

Sound Intensity Measurement

Sound wave graphs are the usual way of representing sound intensity in any digital program, including Final Cut Pro.

Two types of Sound wave representation (Envelopes): Percussive and Sustained.

Percussive are short and sharp, they usually correspond with percussion instruments. Sustained are longer and don't fall off aburptly. They are linked to string instruments, such as cellos.

Decibels is the measurement of sound or electric pressure levels.

There are various reference levels of decibels. The one that is used in digital technology is dBFS. FS stands for Full Scale, because, unlike analog signals, the entire range is available in digital value.

Signal and Noise

0 dB is the ideal recording level. There is some allowance for a higher signal, but most be careful when the sound level move past 0 dB.

It's impossible to get rid of floor noise, that is the lowest level of sound in the environment. Most recordings have sound much higher than the floor, so the listener is unlikely to notice it. However, if your sound was recorded to low, and you enhance it, or simply turn up the volume, the floor noise will become noticeable as a hiss.

Sample Rate

The number of signs a signal is measured per second. Higher sample rate equal better quality because the wave form is closer to capturing more information from the source.

Audio Sample Rates:

8 kHz - 22.225 kHz are used for multimedia files.
32 kHz is generally used with 12-bit audio on DV.
44.1 kHz is use for music CDs and somd DAT recorders.
48 kHz is used by most digital video file formats.
88.2 kHz double 44.1 used for high-resolution audio to be compatible with 44.1kHz.
96 kHz double 48 kHz, the professional standard of audio post-production including music recording.
192 kHz multiple of 48 and 96 kHz highest resolution rate used for professional sound mastering.

Bit Depth

The range of audio samples used in binary numbers (bits) to represent the strength of audio samples. Think of it as rings and spaces between the rings. The more rings in the sampling the better the signal replication.

Bit Depth Rates:

32-bit: used in Final Cut Pro. Should provide a wide range of experimentation and adjustment without distortion.
24-bit: audio industry standard for recording formats.
20-bit: used in some video formats including Digi-betacam and ADAT Type II
16-bit: used by DAT recorders.
8-bit: was used for CD-Roms and the Web. With the increase in bandwidth this format is not as often used.