Luthiers’ tap testing is an informal impulse response measurement

Evidence

An important part of the transient response of a violin is listening to what the body does with the impulse it receives: how does a great violin differ from a mediocre one for sound transiently produced from an impulse? The measure involves cross-correlation (bridge → sound, or bridge to body, as opposed to bridge back to bridge), not autocorrelation, but the procedures for analysis of the response information is very analogous. The informal tap testing and tuning by luthiers is nearly universal, both for sections of the violin before it is assembled, and for the whole after it is assembled. This is clearly a kind of impulse response, which in the case of tapping the bridge, tests the whole chain of events from string to air. Surely there is useful information in this for the trained ear—even more, for a standardized tap and a trained computer—but it seems that the direct use of the impulse response is not traditional for the string family. Systematic differences between violins might be more obvious in the time domain. At the very least, new sorts of features for comparison should become apparent. — Eric J. Heller, Why You Hear What You Hear- An…, 1784

Categorization

• DEFINE: Recasts a familiar craft practice (tapping a violin’s bridge) in impulse-response terms — a bridge between felt practice and formal analysis.
• XREF: Cross-domain parallel with the reader’s notes on soundscapes: expert listening as informal measurement.
• SEED: Article angle: the untapped potential of standardized impulse-response testing as a scientific route to what luthiers already know by ear.