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Slaying Dragons #20 – High resolution?

John Watkinson wonders what high resolution or high definition audio might mean.

In these days of newspeak, words no longer seem to mean what they used to. Resolution and definition are terms used in audio that have been adopted from photography and television, where I believe they still have some meaning. To see what they might mean in audio, we have to start with imaging.

The terms definition and high definition don’t seem to be used in photography, whereas resolution has a long history of use. In a still picture, spatial resolution is a measure of the amount of detail that can be reproduced; in other words the highest spatial frequency that can pass through the device under test, which could be a lens, a film or a sensor. The unit is the number of cycles of modulation that can be discerned in some agreed distance, like a millimetre. The modulation transfer function (MTF) is a graph of modulation depth against spatial frequency.

In a still picture, there is some logic to having higher spatial resolution in the camera than is strictly necessary. The reason is that photographs are often cropped to emphasis the important area or to remove some distraction at the edge. By starting with high resolution, the resolution will still be adequate after cropping.

In a digital still image, three binary numbers describe each pixel, representing the amount of each primary colour. Those numbers have resolution too, but in a different domain…

(contd)
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© John Watkinson

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