Whenever you record somebody screeching in a very high pitched manner, you will usually get distortions. I will link to some examples (warning: LOUD)

Example 1 [48kHz signed 16bit wav]: this almost sounds like it has a robotic voice saying "Wow. Yeah, yeah." over the screaming.

Example 2 [8kHz signed 16bit wav]: here it is the most obvious.

Example 3 [32kHz signed 16bit wav]: here you can hear a single long "sweep" with a slight trill at the end.

This artifact is also sometimes used as a radiowaves/transmission/scanning sort of sound effect. How do you generate a more pure form of this sort of sound, apart from screaming into the microphone and attempting to make it sound less screechy?

If possible and applicable, I would like a low level "nitty gritty details" answer that uses compression/frequency/math to explain this, because I'm guessing it has something to do with those, but I don't know what terms to search for regarding this.


Those are sampling artifacts. The sample rate is too low to cope with the frequencies involved so you get aliasing distortion, where the artificial elements of the digital signal (high frequency components) are aliased with the real signal giving you some very odd outputs.

(From Nyquist Theorem, the sampling rate must be at least double the highest frequency you expect to record)

From earlevel.com:

Consider a digital audio system with a sample rate of 48 KHz, recording a steadily rising sine wave tone. At lower frequency, the tone is sampled with many points per cycle. As the tone rises in frequency, the cycles get shorter and fewer and fewer points are available to describe it. At a frequency of 24 KHz, only two sample points are available per cycle, and we are at the limit of what Nyquist says we can do. Still, those two points are adequate, in a theoretical world, to recreate the tone after conversion back to analog and low-pass filtering.

But, if the tone continues to rise, the number of samples per cycle is not adequate to describe the waveform, and the inadequate description is equivalent to one describing a lower frequency tone—this is aliasing.

In fact, the tone seems to reflect around the 24 KHz point. A 25 KHz tone becomes indistinguishable from a 23 KHz tone. A 30 KHz tone becomes an 18 KHz tone.

In music, with its many frequencies and harmonics, aliased components mix with the real frequencies to yield a particularly obnoxious form of distortion. And there’s no way to undo the damage. That’s why we take steps to avoid aliasing from the beginning.

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  • Ouch, yes. Also note the OP has mixed up 'bitrate' with 'sampling rate' - 8kbps is really 8kHz. – Tetsujin Oct 1 at 10:18

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