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Media & Design Center - Labs, Software & Equipment: Audio Concepts

What is sound?

Sound comes from waves created by vibrations that travel to our ears. Its two main properties are frequency and amplitude.


Frequency refers to the speed of a sound wave and affects its pitch. It is measured in Hertz (Hz), defined as the number of wave cycles per second. High frequency sounds are higher in pitch; low frequency sounds are the opposite.

A sound wave decreasing in frequency from left to right. The bottom left side text says high frequency. The bottom right side text says low frequency.

Human hearing picks up frequencies from about 20Hz to 20kHz. Emphasizing different areas within this range impacts the impression of the sound. The following are simple approximations of the division of the audio frequency range.

20 – 80Hz: Sub-bass; the lowest end of the frequency range where the sound is more 'felt' than 'heard.' Gives power and fullness to a sound, but too much emphasis thickens and muddies it.
80 – 300Hz: Bass; the range of sound that gives an anchor to what we hear. Provides a structure to sound.
300 – 5kHz: Midrange; the area humans are most sensitive to hearing, and where our vocal ranges are. 
4 – 6kHz: Presence; an area that gives clarity to sound. Emphasis here makes things sound closer.
6 – 20kHz: Brilliance; the highest frequency range that contains a lot of harmonics. Emphasis here can give clarity and definition to sound and increase its brightness, but can also increase its sibilance (the harsh sounds from consonants like S and T).


Amplitude measures the size of a sound wave and impacts its loudness. The larger the amplitude, the louder the sound.

Amplitude is measured in the relative unit decibels (dB), which means they require a reference level for it to be understood.

For human hearing, decibels refer to Sound Pressure Level (SPL), where 0dB is the threshold of human hearing. General conversation is about 60dB.

For digital audio, decibels refers to decibels relative to Full Scale or dBFS. Here, 0dB is the highest possible audio level. Sounds that go over 0dB go through what is called clipping, which is a type of sound distortion that results in bad sounding audio (think of when someone yells really loudly in a 'Try Not to Get Scared' video). Digital editing programs like Adobe Audition therefore measure audio levels in negative decibels.

An important distinction to make here is that decibels do not necessarily measure how loud something is. Loudness is a subjective measure, whereas decibels are physical. This means that looking at the audio levels is a more universal measure of how intense something is, which is helpful in keeping audio content from varying wildly between programs. For example, imagine how frustrating and dangerous it would be to constantly adjust your car volume each time the radio played a different song.

When editing digital audio, we recommend keeping the levels between -12dB and -6dB.

Key Concepts for Sound

Sound on screen: Key concepts

Regardless of the film's length or budget, sound represents one of the most important elements to consider throughout all stages of production. Keeping aware of the different sources and types of sound at your disposal can help you use this element to great effect. Check the list below for some essential types of sound used in film. 

Diegetic Sound: This type of sound is heard within the world of the film. The characters on screen can hear it as well as the audience. Some examples of diegetic sound include dialogue between characters, a radio playing music within the same room as the characters, and sounds caused by the characters' actions (ruffling newspaper, for instance, or hanging up a telephone). 

Non-diegetic sound: This type of sound is heard only by the audience, and not by the characters on screen. Some examples of non-diegetic sound include soundtrack music the characters cannot hear, narrative voice-overs, and audience laughter in a sitcom.

Direct Sound: Direct sound refers to audio recorded at the time and place of filming. If a scene is captured using only direct sound, there are no added effects, soundtracks, or dubbing—the sound is captured on set and simultaneously with the scene.

Postsynchronization: This process involves adding audio and sound effects to the scene after recording. Examples include explosions, lasers, and combat sounds commonly heard in action and sci-fi/fantasy films. 

Room tone: This is the sound of a place when no one is talking. Very rarely is there complete silence in a given place; the air conditioner might be running, birds might be chirping out the window, etc. A room sounds different depending on the time of day, as well, so during filming the room tone often changes. This causes subtle but noticeable differences between cuts, so room tone is often recorded separately from the rest of a shoot to use in post, often during cuts in the video to hide the change in sound.

Ambience: This is the opposite of silence; ambience are the sounds you would expect to hear in a given scene, as well as other sounds that help add to the mood. For example, an audio drama podcast might have a conversation that takes place in a cafe. The voice actors would likely not want to record in a cafe for various reasons. But at the same time, a cafe is unlikely to be very quiet with absolutely nothing happening in the background. So editors might add background sounds of people talking, orders being taken and the cash register going off in post. These types of sounds add to the mood of the scene and can be controlled in a way they couldn't if they were recorded directly while filming.

Microphone Polar Patterns

Microphone polar patterns: What are they?

A microphone's polar pattern determines the sensitivity with which it can pick up sounds from different directions. Whether on a live film set or recording music in a studio, choosing the right microphone for the situation can mean the difference between high- and low-quality audio.

Cardioid: Cardioid microphones are great all-purpose tools for recording audio in your environment. The polar pattern of a cardioid mic will pick up a wide range of sound from the front and sides of the microphone. Cardioid microphones are well suited for recording interviews and capturing ambient sound in an environment. The Zoom H1 and Zoom H4n Pro recorders have cardioid microphones that can be checked out at the MDC. The Samson Q2U and the Shure PG58 are cardioid microphones also available for checkout. The Yeti Nano can be set to a cardioid polar pattern or an omnidirectional polar pattern.

Supercardioid and Lobar: Supercardioid and lobar microphones pick up a limited range of sound in the direction they are pointed. They are often referred to as shotgun mics and have narrow polar patterns that pick up audio directly in front of them. They are well suited for isolating specific audio sources when recording for film and can be mounted on top of a camera or held on a boom pole. The Azden SGM-X and Sennheiser ME66 are supercardioid/lobar microphones available for checkout at the MDC.

Omnidirectional: Omnidirectional mics receive sound from any direction with equal sensitivity, resulting in a circular polar pattern. In other words, an omnidirectional microphone will pick up sound from all sides. They are suited to recording musical performances with many people/instruments or a moving target. The Azden WLX-PRO is an omnidirectional mic available for checkout at the MDC. The Yeti Nano can be set to a cardioid polar pattern or an omnidirectional polar pattern.

Shape of sound a cardioid mic picks upShape of sound a lobar shotgun mic picks upShape of sound an omnidirectional mic picks up

Images from Galak76, CC BY-SA 3.0 <>, via Wikimedia Commons.

Audio Recording Equipment

Microphone Rental at the MDC

Want to learn more about the different microphones available at the MDC? Read the list below! 

Already know what you want? Click here to borrow equipment!

Zoom H1 Digital Recorder The Zoom H1 Handy Digital Recorder is an ultra compact field recorder that can record wave files at up to 24 bits and 96 kHz, or MP3 files at up to 320 kbps. It has a 3.5mm mic/line jack. It can be powered by the wired AC adapter or one AA battery . Included: Recorder, AC adapter, SD Card, USB cable.

Zoom H4n Pro Digital Recorders The Zoom H4n Pro Model Handy Digital Recorders are ideal for recording live musical performances, interviews, podcasts, meetings, classes, and seminars. The H4n allows you to record 24 bit/96 kHz digital audio as well as in MP3 format with bit rates up to 320kbps. It has two XLR/1/4″ combo jacks with 48v phantom power to connect up to two external mics or line-level sources. It can be powered by the wired AC adapter or two AA batteries. Included: Recorder, AC adapter, SD Card, USB cable.

Azden SGM-X Shotgun Mic The Azden SGM-X microphone is a shotgun mic that is especially suited for film and video location recording applications, and it can be mounted on top of and connected to any camcorder that is available at the MRC.

Sennheiser Shotgun Mic The Sennheiser ME66 microphone is a shotgun mic that is especially suited for film and video location recording applications, and for picking up quiet signals in noisy environments. It can be connected to either of the MRC’s HD video cameras, and it can be mounted on a boom pole mic stand, which the MRC supplies. Included: Mic, Pistol grip, XLR-M – XLR-F cable OR XLR-F – 3.5mm-M cable.

Azden WMS PRO Wireless Lavaliere Mic This versatile system consists of the WM-PRO belt-pack transmitter, a lavaliere mic, and the WR-PRO receiver. It runs on two 9v batteries. Included: Lavaliere mic, body pack transmitter, camera receiver w/ built-in 3.5mm cable.

Shure PG58 The Sure PG58 mic is a dynamic mic useful for voiceovers, interviews, or creating podcasts. Included: Mic, XLR-F – XLR-M cable or XLR-F – 3.5mm-M cable.

Media & Design Center Staff

The Media & Design Center staff are available to answer your questions on using equipment, finding films, and creating posters or podcasts!  

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Media & Design Center
Undergraduate Library
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Chapel Hill, NC 27599