81825.8.4.1 Ground Follows Signal............................................................ 847
25.8.4.2 Ground Current Summing.......................................................... 848
25.8.4.3 Typical Grounding Problems....................................................... 848
25.8.4.4 Ground Noise in Virtual-Earth Mixers................................................ 849
25.8.4.5 Reactive Ground Effects........................................................... 850
25.9 Signal Switching and Routing............................................................. 850
25.9.1 Relays............................................................................. 850
25.9.2 Electronic Switching.................................................................. 851
25.9.3 MOSFETs and CMOS................................................................ 851
25.9.4 Potentiometric Switching.............................................................. 853
25.9.5 Minimizing Noise.................................................................... 853
25.9.6 Practical Matrix Example.............................................................. 854
25.9.7 Matrix Crosstalk..................................................................... 854
25.9.8 16-Track or 32-Track Routing.......................................................... 854
25.9.9 Processor Control.................................................................... 855
25.9.10 Audio Path........................................................................ 855
25.10 Input Amplifier Design.................................................................. 858
25.10.1 Power Transfer and Termination Impedance.............................................. 859
25.10.2 Optimizing Noise Performance......................................................... 860
25.10.3 Noise Figure....................................................................... 860
25.10.4 Inverse-Frequency Noise............................................................. 860
25.10.5 Optimum Source Impedance (OSI)..................................................... 861
25.10.6 Microphone Transformers............................................................ 861
25.10.6.1 Transformer Characteristics....................................................... 862
25.10.6.2 Common-Mode Rejection......................................................... 863
25.10.6.3 2Microphone Transformer Model................................................... 863
25.10.6.4 Bandwidth..................................................................... 864
25.10.6.5 Common-Mode Transfer.......................................................... 864
25.10.6.6 Input Impedance................................................................ 865
25.10.6.7 Attenuator Pads................................................................. 865
25.10.6.8 Transformerless Front Ends....................................................... 866
25.10.6.9 Line Level Inputs............................................................... 867
25.10.6.10 Electronic Balanced Outputs...................................................... 869
25.10.7 A Practical Microphone-Amplifier Design................................................ 871
25.10.7.1 System-Level Architecture........................................................ 871
25.10.7.2 Input Coupling................................................................. 872
25.10.7.3 Line Level Input Facility.......................................................... 873
25.10.7.4 Common-Mode Rejection Ratio.................................................... 873
25.10.7.5 Minimum-Gain Considerations..................................................... 874
25.10.7.6 The Limiter.................................................................... 874
25.10.7.7 High-Pass Filters................................................................ 875
25.11 Equalizers and Equalization.............................................................. 875
25.11.1 Single-Order Networks............................................................... 876
25.11.2 Single-Order Active Filters............................................................ 876
25.11.3 Changing Filter Frequency............................................................ 878
25.11.4 25.11.4 Reactance and Phase Shifts..................................................... 878
25.11.5 Resonance......................................................................... 879
25.11.6 Resonant Q........................................................................ 879
25.11.7 Bandwidth and Q................................................................... 879
25.11.8 Creating Inductance................................................................. 879