How are Bit Rate & Bit Depth Different?
Hopefully you have already read my earlier post on digital audio vocabulary. There Bit Depth is covered in more detail as well as sample rate and interpolation. However, here I want to clear up the difference between Bit Depth and Bit Rate.
Each sample is stored as digital data, which has a binary value of a 0 or a 1, so it has two possible outcomes. However, if we were trying to sample a sine wave with only two values it would always look like a jagged line each measurement of the digital sample is usually allowed 16 bits (consumer audio standard) to record at a higher resolution.
The bit depth is also know as the dynamic range, the difference between the smallest and largest usable signal (audio amplitude) through a transmission, of any given sample instance. The larger the bit depth the deeper the range or the higher the resolution.
Bit Depth Resolution available for the amplitude of the audio (dynamic range for each digital sample)
- 16 bit – 65,536
- 24 bit – 16,777,216
- 32 bit – 4,294,967,296
This is the measurement of how much data is used per second of audio. To figure this number out you need to know your audio’s Bit Depth and Sampling Rate. Below are the equations for common audio formats and qualities.
Bit Rate = Bits Per Second = (Bits Per Sample * Samples Per Second)*2
Digital Audio for Music
16 bit Wave Audio = (16 bits * 44.1 kHz) = 705.6 kbps (mono audio) * 2 = 1411.2 kbps (stereo audio)
24 bit Wave Audio = (24 bits * 44.1 kHz) = 1058.4 kbps (mono audio) * 2 = 2116.8 kbps (stereo audio)
32 bit Wave Audio = (32 bits * 44.1 kHz) = 1411.2 kbps (mono audio) * 2 = 2822.4 kbps (stereo audio)
Digital Audio for Film
Film uses 48 kHz per second. You can do the math if you are here for film 😉
Calculating File Size
If you want to then calculate file size you would just multiply the kbps of the audio by the number of seconds in the file.
If I have a song that is 4.23 minutes long, that is 253.8 seconds. That multiplied by the industry standard for digital audio (16 bit at 44.1 kHz which is 1411.2 kbps (stereo audio)) we will get a file size of 358162.56 bits. That is roughly 44.8 MB.