Resolution (Bitdepth)

When filming our bouncing ball, we want the camera to take a sufficient number of images per second to reproduce the ball's smooth motion, but we also want each of the images to be distinct and clear so that the ball itself is reproduced as realistically as possible. This is resolution.

Imagine we are using a digital video camera to capture the series of images of the bouncing ball. The larger the number of pixels used for each image, the clearer the ball will be. If we use a small number of pixels--a low resolution--the ball will be fuzzy and indistinct. The higher the resolution, the more realistic the resulting images, and the more convincing the representation of the ball as it bounces.

Resolution in uncompressed digital audio is similar to resolution in a digital photograph. The larger the number of bits used to capture each sample of the sound, the higher the fidelity of the reproduced sound. Digital audio samples are stored in strings of bits called words. The number of bits in each word determines the resolution, or bitdepth, of the digital audio. Typically, the lowest resolution used for digital audio is 8 bits. Compact-disc audio has a resolution of 16 bits, but professional recording studios capture sound using 20-, 24-, and even 32-bit resolutions.

As in digital photography, the trade-off with resolution is storage space. The higher the resolution, the more storage required. Also, for a stereo recording, each channel is sampled separately, so a single sample requires two words. You can use this formula to calculate the size of an uncompressed audio file: size in bytes = sampling rate $\times$ resolution $\times$ number of channels $\times$ number of seconds / 8 (the number of bits in a byte). For example, to calculate the size of a file containing one minute of stereo compact disc audio: 44,100 (sampling rate of 44.1 kHz) $\times$ 16 (resolution, in bits) $\times$ 2 (channels) $\times$ 60 (seconds) / 8 (bits in a byte) = 10,584,000 bytes, or 10.1 MB.^2.1