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Sample Rate and Bit Depth

As previously discussed, analog technology is the processing of electrical signals while digital technology generates unique ‘words’ that are converted into an electrical signal via an audio interface. These words act as location markers mapping out a signal over a period of time that is then converted into electricity.

To determine one of these markers (points) in the audio waveform an X and Y value must be assigned.

The X axis component is called the sample rate, meaning the number of points of a waveform generated per second (AKA Frequency)

The Y axis component is called the bit depth, meaning the level at which a sample is generated at a particular moment (AKA Amplitude)

The faster the sample rate and larger the bit depth the higher the resolution of a digital sound. However, beyond a particular sample rate and bit depth the audible quality begins to plateau. In other words, beyond a particular resolution, the relationship between audible quality and file size becomes disproportionate creating larger file sizes with no increase in audible quality. This resolution threshold is a bit depth of 24 and sampling rate of 44,100 Hz (samples per second). In short 24/44.1kHz. This resolution is considered professional quality audio as any resolution below the optimal sample rate and bit depth will begin to introduce digital artefacts due to a lack of ‘quality’ in the conversion of the digital word into an analog signal.

24-bit/44.1kHz kick drum sample

Sample Rate

Low sampling rates won’t be able to reproduce high frequency content as the wavelength period may be shorter than the sampling rate itself.

Low sampling rate kick drum sample depicts very few frequencies represented at many different amplitudes

Sometimes a sampling rate may be higher than 44,100 Hz but for worthy reasons. One reason may be to code a piece of audio with watermark frequency content above 20kHz for copyright purposes. Another reason may be for professional studio standards as really high end equipment will be able to produce detailed frequency content therefore a higher resolution is worked with. Finally, another reason will be for simple mathematic compatibility within the film industry. Typically, a sampling rate of 48kHz is used since it is better divided with the frame rate of the video creating far more simplistic mathematics upon converting and exporting.

Bit Depth

Low bit depths are utilized when exporting demos, snippets or mp3 versions of a song as low bit depths (lower than 24) decrease the size of an audio file drastically compared to that of a 24-bit audio file. Generally, 1 minute of WAV audio requires 15MB of hard drive space while 1 minute of MP3 audio requires 1MB.

Low bit depth kick drum sample depicts many different frequencies represented at very few specific amplitudes.

  • Formats that use 24-bit depths are .wav, .aif and .flac

  • Formats that use 16-bit depths are .mp3 and .aac

As a general rule of thumb, when producing music within a DAW, keep the sample rate and bit depth consistent whether you are working in 16 or 24 bit. Not only is it good information to know, it also helps with selecting the best export methods as far as resolution and dither settings.

During mixdown, larger bit depths allow for more accurate balancing when adjusting track faders. The reason is because the bit depth is the amplitude component of a digital signal, therefore low bit depths offer less volume positions when mixing. In other words, the track fader is divided up into a number of positions based on the bit depth. At larger bit depths, the more number of positions for the volume to be.

Lo-fi genres utilize a lower bit depth and sample rate to capture the character of low fidelity as a creative decision. It introduces artefacts causing a glitchy, grainy type sound depending on the resolution itself.

A small bit depth produces a digital artefact known as ‘quantization error’ while a low sample rate produces a digital artefact known as ‘aliasing’. They produce slightly different qualities in a digital signal and knowing the difference between the two will better direct you towards the source.

Experiment with Ableton’s “Redux” device and get creative with particular digital artefacts associated with low sample rates and small bit depths!

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