process worked well with playback via a conical stylus, typical of most phonograph cartridges prior to about 1964. However, if one played a Dynagroove record with an elliptical-shaped stylus, this pre-distortion became audible. As the decade of the 1960s progressed, high quality playback cartridges increasingly used elliptical styli. This development made tracing compensation obsolete by about 1970, and RCA quietly stopped using the technique. The other technique used with Dynagroove was a dynamic equalizer, which varied the tonal quality of the recording according to the loudness of the sound. Loud passages were reproduced with little tonal change, but softer passages had boosted lows and highs. Harry Olson, RCA's chief engineer, advocated the use of dynamic equalization for two reasons: the process would help keep softer musical passages above the noise floor of the LP disc; and music processed through the dynamic equalizer would, in theory, tend to have a tonal balance closer to what the listener would hear in a live performance. This latter characteristic was based on Olson's work comparing consumer playback of recorded music to live musical performance. Olson found that most people listened to records at sound levels about 20 decibels lower than actual live performances. Human hearing is not linear with level change, but tends to perceive softer sounds as having less bass content. The dynamic equalizer was an attempt to compensate for the reduction in bass that would be perceived by listening to records at typical levels. As noted above, critical reaction to this technique was mixed. RCA stopped using dynamic equalization about the same time they stopped using tracing compensation in 1970. Dynagroove promotional and regular records Partial list Van Cliburn/Fritz Reiner/Chicago Symphony Orchestra Beethoven: Piano Concerto no. 4 in G major, op 58. 1963 original RCA, Made in Germany shortly after under LSC-2680-B (stereo) and LM-2680-C (mono) This Is Dynagroove! (1963) PRS-140* Sid Ramin - "Swanee" Marty Gold - "I'll Remember April" Dick Schory - "Take the "A" Train" Hugo & Luigi Chorus - "I Love You" Peter Nero - "Granada" Arthur Fiedler/Boston Pops - "Star Dust" Erich Leinsdorf/Boston Symphony - "Mahler: Symphony No. 1 (Finale)" Arthur Fiedler/Boston Pops - "La Sorella" Charles Münch/Boston Symphony Orchestra - "Debussy: Nocturnes, Fêtes" Leontyne Price & Richard Tucker - "Puccini: Madama Butterfly Act 1: Love Duet" Morton Gould - "Sibelius: Findlandia (Finale)" The Sound Of Tomorrow (Buick Highlighter) (1963) SP-33-204/SPS-33-204* Peter Nero - "Londonderry Air" Marty