Insider with Robert Harley — What a test sounds like

The Heyser Box

Jan 5 – I was talking to Absolute Multimedia CEO Tom Martin recently about why subwoofers sound so different (and why we can’t quantify those differences through measurement). He suggested that we’re so accustomed to thinking in terms of steady-state test signals that we overlook time-domain behavior. This is a natural tendency for human beings; we don’t live in the temporal world of milliseconds.

This led me to relate the story of The Heyser Box, named after the great audio thinker Richard Heyser (inventor of Time Delay Spectrometry, among other things). The Heyser Box has one input and one output. When measured on a test bench, it has no distortion, no phase shift, ruler-flat frequency response, wide bandwidth, and all the other attributes we consider ideal performance. Indeed, the box appeared on the test bench to be a piece of wire.

But when you put music through The Heyser Box and listen to it, the sound is so distorted that the music is unintelligible.

How could something measure perfectly and sound so horrible? The secret is that a circuit inside the box identified the steady-state nature of the sine waves used in bench testing and closed a relay connecting the input to the output. The box was indeed a piece of wire. But when the circuit detected the continuously changing dynamic nature of music, the relay opened and closed quickly, chopping up the waveform and rendering the signal unlistenable.

The lesson that The Heyser Box brilliantly teaches is that assumptions made about audio equipment performance on the test bench don’t apply to equipment reproducing music. Audio is the only field in which the products are tested under conditions (steady-state sine waves) that bear no relationship to how the products will be used in the real world.

This Week’s Audio Quotation “The easiest thing in the world is to play an LP record incorrectly.”

âDoug Sax, founder of The Mastering Lab, co-founder of Sheffield Lab, father of the modern direct-to-disc recording, and mastering engineer extraordinaire.