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High-pass filters, low-pass filters - shouldn't they be low-cut and high-cut?

Whoever invented this stupid terminology should be force fed with Brussels sprouts for a fortnight. Even the 'experts' can get it wrong.


OK quickly now - which band of frequencies does a high-pass filter control?

If you answered correctly within half a second then you have an agile brain indeed. Most of us ordinary folk have to consider carefully before stating that a high-pass filter controls low frequencies.

Yes it does! The more you think about it the more confusing it gets. It's like asking what the right time is when a clock is showing twenty-past but it's forty minutes slow.

A high-pass filter controls low frequencies. High frequencies pass unaltered.

A low-pass filter controls high frequencies. Low frequencies pass unaltered.

Now here is the embarrassing thing. Despite having experience in audio training for almost twenty-four years, we managed to get this wrong in one of our texts.

Specifically we said that a high-pass filter rolls off frequencies above its cut-off frequency. That should of course have been below.

OK, we've eaten Brussels sprouts for a fortnight, and corrected the error.

But we do humbly suggest that it's the terminology that is wrong. We suggest the following...

A low-cut filter controls low frequencies.

A high-cut filter controls high frequencies.

This terminology makes it clear what the filter does that makes a difference, rather than what would happen even if the filter were not inserted into the signal chain.

Now, if only we can get everyone else to agree...

By David Mellor Friday February 26, 2010
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