Deep diving in bit depth

By | April 5, 2021

What is bit depth?bitdepth_16.png.0699a07aef17fcc1c6b468a6a990ed3d.png
Bit depth is a way of digitally presenting sound with evenly distributed samples (measuring points). In a sound sample with 16 bits PCM (pulse code modulation), each sample contains one of a number of values ​​evenly distributed along a timeline. Each bit can have two states, 1 or 0. Together with more bits, a value is created where, for example, 4 bits have 16 states and 16 bits have 65536 states. Each sample is then quantized to the nearest possible digital value. Each sample is then plotted according to a time course defined by the sample rate.

Bit depth and masteringbitdepth_24.png.b127ec7884cbeba52fe068ffa1fe5346.png
It can be difficult to hear the difference in sound in 24 or 16 bits, especially if you do not know what to listen for. In mastering, it is important to know the differences and how the different problems that can arise during a conversion between the different bit depths may sound. Not only to know how a rendering can sound but also to be able to make as relevant and unproblematic decisions as possible during the mastering process.

Difference between 16 and 24 bits
The biggest difference between 16 and 24 bits is that 16 bits have a lower SNR (signal to noise ratio), ie the range between the lowest noise (noise floor) and the maximum amplitude. 16 bits have an SNR of 96dB and 24 bits have an SNR of 144 dB. At 16 bits, the range is therefore reduced, which is mainly heard by the fact that the lowest noise in the background is higher.

To distinguish bit depth
When listening to music, it is difficult to hear the difference between 16 and 24 pieces, but there are ways to distinguish them. It is easiest to hear when a fade out at the end of a piece of music in 16 pieces. During fading, you simultaneously turn up the volume on your stereo and then hear the noise earlier than with a 24-piece piece. The threshold between sound and silence is also reminded by the fact that the sound fades out less softly and has a more sudden transition to “absolute silence”.

It is important that the bit reduction is the last thing that happens in a mastering as other modifications in the mastering process can underline the problems or even worsen the end result. Therefore, always ask the mixing technician to bounce / render the music at an unreduced bit depth.

NOTE! The images above are not to scale

Joel Nevrup
Mastering Technician, Spectrum Mastering | instagram | facebook