Noise in 8-bit recordings

admin: First posted on 2016 04 07

mic, 2016 04 07: This is a note on a topic that most would be familiar with but is worth noting anyway. We are currently testing the recording and playback of 8-bit waves and we wanted to note that, yes, there is noise in 8-bit recording. This is normal. It is due to the natural limits on what 8-bit data can represent. With 8 bits, a number can take at most 256 values (2 to the power of 8). Let's say these values are 0 to 256, since the convention is that 8-bit PCM wave data is unsigned. Here, the "zero" of the signal will be 128 and the maximum peak amplitude of the signal will be 128 as well.

When a signal is digitized, values must be rounded. If the value of the analogue signal at a specific sample comes at 35.6, this value may be recorded as 35 (or 36, depending on the digitizing equipment). So, there is an error during this quantization, that may be as high as 0.5. In other words, the signal to noise ratio created just because of the quantization, in decibels, is 20 log₁₀(0.5 / 128, 10) = -48 dB, which is quite audible. When working with 8-bit data, we do not have much choice, but to accept the noise that is inherent in the quantization.