The earliest horns had no valves and could only play notes in their overtone series. Then 18th-century German musician A.J. Hampel discovered that by partially or fully closing the bell with his hand, he could alter the pitch and produce fully diatonic scales. While today's valved horns can play chromatic scales throughout their range without hand-stopping, some modern composers call for a fully stopped horn to produce a distinctive nasal timbre. And many horn players will occasionally use hand stopping for quick pitch correction on the fly.