If we apply a gentle low-pass filter to eliminate everything above, say 22 kHz, we will also slightly reduce the level of audio as much as an octave below 22 kHz, or 11 kHz. Unfortunately, low-pass filters have some side effects. This low-pass filter is referred to as an anti-aliasing filter. Audio aliases are frequencies that are reflected below the Nyquist frequency and sound like strange non-musical harmonics.Īnalog to digital converters can apply a low-pass filter before sampling so that no audio above the Nyquist frequency enters the A-D converter. This effect happens when the wheel’s speed approaches the frame rate of the video. When we film a wheel with spokes that starts to spin and its rotational speed increases, it begins to look like it slows and then spins backward. Audio-frequency aliasing is much like the wagon-wheel effect seen in videos. If we attempt to record audio frequencies above half the sample rate (also called the Nyquist Frequency), audible artifacts called aliasing can occur. Likewise, a 96 kHz sample rate allows for 48 kHz of audio bandwidth. This means that with a sample rate of 44.1 kHz, we can record audio signals up to 22.05 kHz. The Nyquist Theorem states that the highest audio frequency we can record is half of the frequency of the sampling rate. The sample rate also defines the high- frequency response of an audio recording. Sample rate defines how many times per second we sample, or take a measurement of, an analog audio signal as it is converted into a digital signal. In another article, we cover the ins and outs of bit depth. This article covers the basics and best practices for setting sample rates. We are all familiar with the two digital audio file descriptors sample rate and bit depth, and though these specifications seem routine I often get questions from producers and engineers about the optimum settings for a given project.
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