Last week we delved into the theory of ‘Sample Rates’ and how they are important to the overall quality of your audio recordings. This week we will explore the knowledge and facts of the other important figure related to your audio quality; Bit Depth.
According to our friends at Wikipedia “In digital audio, bit depth describes the number of bits of information recorded for each sample. Bit depth directly corresponds to the resolution of each sample in a set of digital audio data. Common examples of bit depth include CD quality audio, which is recorded at 16 bits, and DVD-Audio, which can support up to 24-bit audio.
Before we can discuss Bit-Depth and the many side notes that accompany this subject, we first must have a basic understand of how digital conversion works. A microphone captures a signal by moving its diaphragm back and forth to generate an electrical current that is captured and amplified through a microphone preamplifier. The current passes from the preamp to the analog to digital converter, which converts the analog signal into a piece of digital information. After this signal passes through the digital processor, it captured by our recording sequencer and stored on a hard drive. The signal is then taken from our storage device, and pushed through the outputs of recording interface which passes through the digital to analog converter, creating another electrical current that causes our monitors to push and pull air at a rapid rate, generating waveforms that are captured by another diaphragm (our ears) perceived by our brains as sound. Simple…
If any of you have every programmed a drum track, you will have heard of the term quantization and associated it simply with pulling your midi notes into time with a grid. Quantization in relation to Bit Depth is a similar process to quantizing a beat; only with this we are quantizing our sample to different ‘bits’ to make up our audio data.
Let’s simplify this as best as we can. When you record audio, every sample (44,100 per second for example) must be assigned to a piece of information called a ‘bit’. Samples cannot fall in between ‘bits’ (quantization error), so they are ‘quantized’ to the nearest bit of information, above or bellow where the sample falls in ‘amplitude’ (the height of the waveform).
The more bits there are to assign to each sample, the greater the resolution of the waveform will be created. Recording in 24-bit gives your sample more bits to be quantized to, and creates a smoother waveform, where recording in 16-bit gives your sample less bits of information to be created with, resulting in a waveform that looks square. It is always best to record in 24-bit and later convert your recording to 16-bit after applying an intentional noise called ‘Dither’.
Dither is used to randomize ‘quantization error’ – which is the difference between the actual analog value, and the quantized digital value. Dither is an inconceivable noise used to help quantize the samples that fall beneath the dynamic range of what the digital converters can actually replicate.
There is so much more to learn in regards to digital audio than what this short blog is able to explain in fine detail. If it’s something you are interested in learning about, do some research for yourself and expand your learning. Knowledge is power.