Dynagroove

Dynagroove is a recording process introduced in 1963 by RCA Victor that, for the first time, used analog computers to modify the audio signal used to produce master discs for LPs. The intent was to boost bass on quiet passages, and reduce the high-frequency tracing burdens (distortion) for the less-compliant, "ball" or spherical-tipped playback cartridges then in use. With boosted bass, tracing demands could be reduced in part by reduced recording levels, sometimes supplemented by peak compression. This added top-end margin permitted selective pre-emphasis of some passages for greater perceived (psychological) brilliance of the recording as a whole. As with any compander, the program material itself changed the response of the Dynagroove electronics that processed it. But, because the changes were multiple (bass, treble, dynamic range) and algorithmic (thresholds, gain curves), RCA justifiably referred to the analog device as a computer.

RCA claimed that Dynagroove had the effect of adding brilliance and clarity, realistic presence, full-bodied tone and virtually eliminated surface noise and inner groove distortion. In addition, Dynagroove recordings were mastered on RCA magnetic tape. Hans H. Fantel (who wrote liner notes on the first Dynagroove releases) summed it up with, "[Dynagroove] adds up to what is, in my opinion, a remarkable degree of musical realism. The technique is ingenious and sophisticated, but its validation is simple: the ear confirms it!"

The process was not received well by some industry commentators, with many audio engineers of the time referring to Dynagroove as "Grindagroove". Dynagroove was also sharply criticized by Goddard Lieberson of the competing label Columbia Records, who called it "a step away from the faithful reproduction of the artist's performance;" and by Harry Pearson, founder of The Absolute Sound, who termed it "Dynagroove, for that wooden sound." Another noted detractor of Dynagroove was J. Gordon Holt, the founder of Stereophile magazine, who in December 1964 wrote a highly unfavourable article entitled "Down with Dynagroove!" Holt, a noted audio engineer and writer of the 1960s and 1970s, slammed Dynagroove as introducing "pre-distortion" into the mastering process, making the records sound worse if they were played on high-quality phono systems.

Holt was technically correct, as the Dynagroove process used tracing compensation, which pre-distorted the record groove to cancel out the distortion created by playback with a conical-shaped phonograph stylus, which could not track the record groove accurately in the high frequencies, especially in the inner grooves of an LP. The 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.