Understanding Sample Rate, Bit Depth, and Bitrate

By Kevin Graham

There are plenty of important technical terms in the world of video production: resolution, frame rate, aspect ratio, codec, interlacing, color space, etc.

In addition, there are a few relevant audio terms that every filmmaker should know. This video is going to focus on understanding sample rate, bit depth, and bitrate.

Sample Rate

The sample rate of a digital audio recording refers to the amount of times per second that the signal is captured (similar to a video’s frame rate).

You can think of a sample as a very tiny slice of audio.

According to a widely-followed principle known as the Nyquist Theorem, a signal can be perfectly reconstructed when it’s sample rate is at least twice as high as the highest frequency (in other words, pitch) in the sound being captured.

The human ear can hear up to approximately 20kHz, which is why 44.1kHz and 48kHz are the most popular sample rates in media today.

In video, 48kHz is the standard.

Bit Depth

While sample rate refers to the amount of samples contained in an audio recording, bit depth refers to the amount of binary digits in each one of those samples.

In other words, bit depth determines how closely each sample resembles the original sound, in terms of how many levels of audio are possible within that sample..

The main benefit of a higher bit depth is a higher dynamic range in your recording.

Generally, each bit represents 6dB of dynamic range, so a 16-bit file amounts to 96dB of dynamic range, 24 to 144dB, and so on.

For video, a bit depth of 24 bits is industry-standard.

Bitrate

This is probably the most confusing of these three terms. Bitrate refers specifically to the data throughput of a compressed file (such as an mp3) per second during playback.

This is different from the sample rate, which refers to the amount of samples captured each second during the recording process.

The more bits per second, the higher-quality the audio file will be. Most CDs have a bitrate of 1,411 kilobits per second (Kbps), and mp3s usually range from 96 Kbps to 320 Kbps.

For the average listening system, 320 Kbps is more than enough.

A basic understanding of these technical terms, and knowing the industry-standard settings for each, will go a long way during the export process.

Kevin is the Music Director and Lead Composer at Filmpac