Dynamic Range Compression for Tape Recording of Noise Data
Byron E. Blanchard · The Journal of the Acoustical Society of America · 1973
Conventional approaches such as the Dolby or DBX dynamic range compressors for tape recording are unsuited for noise data recording because the expansion process has an inherent time lag relative to the compression. The time lag occurs because the expander gain is controlled by rectified and averaged compressed signal. A system has been developed to permit exact tracking of the compression and expansion gains even in the transient case. An FM signal representing compression gain command is recorded on a separate tape channel. On playback, the output of an FM discriminator controls the expander gain. The lag of the low-pass filter following the discriminator is matched by an identical filter in the compression circuit between the compression gain command and the gain block. Input signals over a 90-dB range are accommodated and the compression and expansion track within 1 msec.