Noncomplementary_audio_noise_reduction_system

Published:2009/7/23 21:15:00 Author:Jessie | From:SeekIC

Figure 1-49A shows the block diagram, and Figs. 1-49B and 1-49C show the full schematic details of noncomplementary or dynamic noise-reduction (NR) systems. Complementary NR systems require that certain frequencies be emphasized during recording, then de-emphasized during playback in a comple-mentary mode. That is, if highs are emphasized during recording, highs are de-emphasized during playback. These noncomplementary circuits can be applied to any stereo audio system, without regard as to how the material was recorded.Both the left and right audio paths are controlled by signals derived from the mixed audio input (after filtering, amplification, and detection), all of which occurs in the LM1894. The circuits must be placed immediately after the source preamp, and before any circuit that includes user controls (volume, tone, etc.). L8 in Fig. 1-49C is part of a 19-kHz notch filter, and is adjusted to remove the FM pilot signal. R1 and R2 in Fig. 1 -49C set overall gain, as does the 1-kΩ pot in Fig. 1-49B. The 1-kΩ pot is adjusted for best noise reduction of a given program material. Figure 1-49D shows the PC layout for the circuit of Fig. 1-49B.



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