Fundamentals of Audio Production

1. Fundamentals of Audio Production Chapter Nine: Audio Processors and Processing Fundamentals of Audio Production Chapter 9

2. Types of processing • Loudness processing • Dynamic processing • Frequency processing • Temporal processing • Digital processing • Noise reduction processing Fundamentals of Audio Production Chapter 9

3. Loudness processing • Devices or circuits that add gain are “active” devices • Most audio devices include a gain stage • “Unity gain” means that the output level is equal to the input gain of the device or circuit Fundamentals of Audio Production Chapter 9

4. Loudness processing • Microphones have extremely low level outputs and require 40 decibels or more of amplification to be raised to “line level” • Microphone pre-amplifiers raise the level to line level • Power amplifiers then raise the level several more times to a level high enough to drive loudspeaker voice coils Fundamentals of Audio Production Chapter 9

5. Loudness processing Fundamentals of Audio Production Chapter 9

6. Loudness processing • Decreasing gain is easily accomplished using attenuators – such as potentiometers • Potentiometers are actually variable resistors • Adding more resistance lowers the level or volume of the signal Fundamentals of Audio Production Chapter 9

7. Potentiometers As the wiper is moved further from the current input, the resistance is increased and the volume level is decreased. Fundamentals of Audio Production Chapter 9

8. Potentiometers As the wiper is moved further from the current input, the resistance is increased and the volume level is decreased. Fundamentals of Audio Production Chapter 9

9. Potentiometers Fade down – more resistance – less volume Fundamentals of Audio Production Chapter 9

10. Pads • Pads are passive devices – requiring no power and adding no gain • Pads provide gain reduction by adding resistance • The amount of gain reduction is fixed • Rated in number of decibels of reduction Fundamentals of Audio Production Chapter 9

11. Pads Switchable -10 db pad on condenser microphone Fundamentals of Audio Production Chapter 9

12. Dynamic processors • Limiters • Compressors • Noise gates • All allow users to “automate” controlling levels Fundamentals of Audio Production Chapter 9

13. Limiters • Sometimes called “peak limiters” • Allows user to set threshold and output level • When signal exceeds the threshold level, the limiter decreases the signal – prohibiting it from exceeding the preset output level • Often used in broadcasting Fundamentals of Audio Production Chapter 9

14. Compressors • In addition to adjustments for threshold and output- • Also adjustments for ratio of reduction • Ratio of 2:1 provides 2 db of reduction for every db over threshold • Ratio of 10:1 provides 10 db of reduction for every db over threshold • Smaller ratios for more natural sound Fundamentals of Audio Production Chapter 9

15. Compressors • Also have user adjustable attack times • How quickly the gain reduction engages • May also have adjustable release times • How long the signal reduction persists Fundamentals of Audio Production Chapter 9

16. Noise gates • Provide “all or nothing” signal passage • Gate opens when the signal reaches the threshold level and allows signal to pass • Gate closes when the signal falls below threshold and all signal flow stops • In use: gated drum mikes will keep unwanted sounds from leaking in to recording Fundamentals of Audio Production Chapter 9

17. Frequency processors • Filters • Passive devices for cutting frequencies • Equalizers • Active devices for boosting or cutting frequencies Fundamentals of Audio Production Chapter 9

18. Filters • Shelving filters cut a large band of frequencies • High pass, low pass and band pass Fundamentals of Audio Production Chapter 9

19. Filters • Notch filters remove a narrow band of frequencies • Comb filters remove several narrow bands Fundamentals of Audio Production Chapter 9

20. Equalizers • Shelving equalizers boost or cut a wide band of frequencies Fundamentals of Audio Production Chapter 9

21. Equalizers • Sweep equalizers boost a range frequencies by a set amount of gain • The range of frequencies may be user-adjusted or “swept” Fundamentals of Audio Production Chapter 9

22. Equalizers • Graphic equalizers provide a visual or “graphic” representation of the equalization curve • Graphic equalizers are described by the interval between center frequencies of the user controls • e.g. full octave, one-half octave, one-third octave Fundamentals of Audio Production Chapter 9

23. Graphic equalizers Fundamentals of Audio Production Chapter 9

24. Graphic equalizer Fundamentals of Audio Production Chapter 9

25. Parametric equalizers • Parametric equalizers allow the user to define • The frequencies that are being affected • The bandwidth of frequencies being affected, called the “Q” • The amount of boost or cut being applied Fundamentals of Audio Production Chapter 9

26. Parametric equalizers • The controls on a parametric equalizer Fundamentals of Audio Production Chapter 9

27. Parametric equalizer Five band parametric equalizer Fundamentals of Audio Production Chapter 9

28. Temporal processors • Alter the “time” relationships of audio signals • Simulate the effects resulting from the lapse of time when sound pressure waves travel through space • Most common temporal effects are “delay,” “echo,” and “reverberation” • Temporal effects help the listener aurally define the acoustic space Fundamentals of Audio Production Chapter 9

29. Delay • The time offset between a sound and the repeat of that sound • In nature, a result of the reflection of the sound wave • Early delay devices were electro-mechanical • Signal was routed through an extensive electrical path which introduced time delay Fundamentals of Audio Production Chapter 9

30. Delay (effects send) (effects return) Fundamentals of Audio Production Chapter 9

31. Delay Click on the speaker icon to hear a dry signal Click on the speaker icon to hear an example of delay Fundamentals of Audio Production Chapter 9

32. Echo • An echo is generally defined as a single discrete reflection of a sound wave • A result of the time that passes as the sound wave travels to a distant reflective surface and then back to the listener • Echoes can be repeated – but will still be separate and distinct sounds if separated by enough time Click the speaker icon to hear an example of echo Fundamentals of Audio Production Chapter 9

33. Echo • Early echo devices used tape technology • The “Echoplex” employed a loop of tape and a movable playback head to alter the period of delay between the live sound and the echo Fundamentals of Audio Production Chapter 9

34. Reverberation • A complex effect resulting from a series of reflections arriving at the listener’s ears separated by very short intervals • The reflections appear to be a single sound that can be sustained over a long period of time • Reverberation is added to recordings to simulate various acoustic environments Fundamentals of Audio Production Chapter 9

35. Acoustic reverberation • Reverb chambers used speakers and microphones to create and add reverberation • Sound played from a speaker in a hard-surfaced room was captured by a microphone and returned to console for blending with the “dry” sound Fundamentals of Audio Production Chapter 9

36. Acoustic reverberation Reflected sound Loudspeaker Microphone Reflected sound Effected signal Dry signal Console Fundamentals of Audio Production Chapter 9

37. Electro - mechanical reverberation • Spring reverberation • A spring suspended under tension is vibrated by a transducer • Other transducers along the length of the spring convert the vibrations back into sound that are delayed by varying times Fundamentals of Audio Production Chapter 9

38. Spring reverberation Fundamentals of Audio Production Chapter 9

39. Plate and foil reverberation • Both plates and foil reverb devices are similar to springs • Use transducers to convert sound into vibrations in metal plate or foil stretched under tension • Other transducers convert the vibrations back into sound Fundamentals of Audio Production Chapter 9

40. Electronic analog reverberation • Analog delays used Bucket Brigade Delay (BBD) chips • BBD chips named for their similarity to firemen bucket brigades – passing buckets of water from hand to hand • BBD chips store electrical charges in a series of capacitors – charge is passed from “bucket to bucket” Fundamentals of Audio Production Chapter 9

41. Electronic digital reverberation • Digital signal processing (DSP) • Audio is first converted in binary data • Data is held in temporary memory locations in a delay circuit • Data is then released and sent onward to a subsequent memory location • The circuits through which the data is shifted are called “shift registers” Fundamentals of Audio Production Chapter 9

42. Electronic digital reverberation Click on the speaker icon to hear an example of reverberation Fundamentals of Audio Production Chapter 9

43. Flanging and chorusing • Effects created by very short time delays • “Flanging” named for practice of dragging a finger on the flange of a tape reel • Flanging and chorusing are “phase shift” effects • The signal is split and sent through a circuit that introduces slight variable delay • Then signals are re-combined with slight phase shifting Fundamentals of Audio Production Chapter 9

44. Flanging and chorusing Click on the speaker icon to hear an example of phasing Click on the speaker icon to hear an example of flanging Click on the speaker icon to hear an example of chorusing Fundamentals of Audio Production Chapter 9

45. Harmonizers and pitch shifters • Pitch shifters sample the frequency of the incoming signal, and then raise or lower the output frequency • Harmonizers combine the shifted signal with the input signal to create multiple harmonies Fundamentals of Audio Production Chapter 9

46. Noise reduction • Noise reduction circuits were once merely shelving filters or band pass filters • Low pass filters would reduce tape hiss • High pass filters would reduce rumble • Advanced digital noise reduction algorithms allow users to sample a sound, designate it as noise, and then eliminate it from the signal Fundamentals of Audio Production Chapter 9

47. Forensic audio • Forensic audio makes use of the various signal processors and algorithms to enhance audio recordings for investigative purposes Fundamentals of Audio Production Chapter 9