PA System and its operation, Audio recording and Editing for Music Teachers

1. PA System and its operation, Audio recording and Editing for Music Teachers

2. MUSIC AND ENGINEERING:CORRELATION • They both deal with vibrations and harmonics. Music used the vibrations of strings, memberanes, vocal cords etc to make notes which are combined to form chords and music. Engineering must account for vibrations and harmonics which occur naturally from movement in the earth, the wind and other forces. If these vibrations are not accounted for then they can be destructive even catastrophic. • While a simultaneous interest in a science like engineering and an art like music may seem disparate, studies have shown that music stimulates right brain function, enhancing the ability to solve logical and mathematical problems. 

3. What is music in engineering terminology? • The art of arranging sounds in time so as to produce a continuous, unified, and evocative composition, as through melody, harmony, rhythm, and timbre • an art of sound in time that expresses ideas and emotions in significant forms through the elements of rhythm, melody,harmony, and color.

4. Where is sound? Sound waves occur in the air or in any elastic medium, but Sound occurs in the BRAIN!!! Understanding AUDIO Which is the best and most important audio monitor? None other than the Ear!!!

5. Sound and its characteristics • Physical: Sound can be defined as a wave motion in air or other elastic media. • Psychophysical: Excitation of the hearing mechanism that results in the perception of sound [sensation].

6. How sound is produced? • Energy in the form of sound is produced when a vibrating surface or object is contact with the air. • Sources of sound • Vocal • Plucked strings • Air column • Vibrating plate

7. How sound is perceived? • Travel of sound wave and physical stimulation of ear. • Physiological and psychological processing and perception in ear and brain (psychoacoustics) resulting from nerve impulses stimulating the acoustic cortex of the brain.

8. Sound attributes • Amplitude Loudness • Frequency Pitch • Spectrum Timbre • Duration Length • Phase Distance travelled by the • wave at the given time Physical Perceptual

9. Basic Components of PA & Recording System Microphones Mixing Consoles Loud Speakers Recorders

10. Microphones: Types of microphones: • Technology • Dynamic • Condenser • Pattern • Cardioid • Omni directional • Bi directional

11. Dynamic microphones • Versatile and ideal for general-purpose use. • Relatively sturdy and resilient to rough handling. • Better suited to handling high volume levels, such as from certain musical instruments. • Unlike condensers, they have tailored frequency responses to suit particular applications. • Preferred for spoken word, vocals and instruments that produce loud sound.

12. Condenser microphone • Condenser microphones have a flatter and broad frequency response than dynamics. • Produce high level signal, hence more sensitive and responsive than dynamics. • Well-suited for capturing subtle nuances in a sound. • They are not ideal for high-volume work, as their sensitivity makes them prone to distort. • Condensers are preferred for string instruments for capturing their dominant harmonics. • They need power from a battery or external source. • Likely to be affected due to shelf storage, humidity, temp variations. • Capacitor mics capture the sounds of acoustic instruments most accurately, working much more effectively at the high end of the audio spectrum

13. CARDIOID, OMNI DIRECTIONAL & BI DIRECTIONAL MICROPHONES BI DIRECTIONAL MICROPHONES

14. Vocal miking Vocals are perhaps the most difficult source to mic. Each vocalist is different due to variation in the dynamic range within a single performance They tend to move their heads. Problem with the proximity effect

15. Vocal positions

16. Choral singing

17. Miking the instruments

18. Miking Instruments GENERAL MIC THEORY: • A real instrument is not a point source of sound -- what we hear is a blend of an infinite number of sounds emanating from all parts of the instrument. • This means that if the mic is too close to the instrument, you only capture part of the sound, but on the other hand, if you put the mic too far away, not only will you be struggling for level, you'll also pick up more reflected room sound than you do direct sound. In some rooms, this can sound good, but in most cases, you end up with a boxy, distant sound that is lacking in detail and presence. • A good compromise is to space the mic away from the instrument by a distance similar to the longest dimension of the instrument. • In the case of a guitar, you can say that the sound-producing part of the instrument is just the body (not strictly true) and put the mic around 40mm from the body, or you could accept that some sound comes directly from the strings and neck and put the mic at up to 80mm from the guitar. • In the case of a typical drum kit, the mics would be placed 150mm or so in front of the kit. Though this rule isn't perfect, it will usually get you into the right ball park very quickly, and it's come in very handy when I've been asked to record unusual instruments for which no textbook method exists.

19. Miking Instruments BASS GUITAR: Most people now record the bass guitar using a DI box or recording preamp. The best miked bass sounds are usually achieved by putting a good dynamic mic 200 or 300mm from the speaker grille and playing normally.  ELECTRIC GUITAR: At one time, no serious engineer would record the electric guitar any other way than with a mic, but now guitar preamps seem to be just as popular. When you mike an amp, you'll notice the sound changes as you move the microphone around the speakers. For rock sounds, put a dynamic mic right up against the grille, or for a more mellow sound, move it away from the centre of the speakers KEYBOARDS: Miking up a keyboard, the trick seems to be to work in stereo with one mic either side of the cabinet, facing the speaker grilles. It is important not to set the mics too close, otherwise wind noise may be picked up from the rotors, and the benefit of the room reflections will be lost. An initial distance of 300 to 400mm should get you in the right area. BEAT IT — MIKING UP DRUMS: BASS DRUM:The dynamic mic should be about 200mm from the beater, suspended inside the drum shell on a boom stand that isn't physically touching any part of the shell. For the snare drum, use a dynamic mic around 50mm from the edge of the drum, and about 50mm above the head.

20. What is phasing? • Phase is the time difference between to similar waveforms. • When two signals are close in frequency and amplitude (level) but out of time with each other, there is a phase difference. • Two sound waves with equal phase difference is called in-phase • Two sound waves with difference of 180 degrees is called out of phase • Sound waves at other phases than the above two, give rise to a phenomenon called comb filtering

21. When phasing occurs? • If more than one mic is used for recording a single source, phase becomes an issue. • Phasing problems occur when a sound reaches different mics at different times. • The more mics you have open, the greater the chance for there to be phasing issues.

22. Phasing & Multiple Microphones • If multiple mics on at the same time, use the 3:1 rule: • Separate mics at 3x the distance from talkers • Comb effects aren’t noticable

23. Audio Mixers Or Mixing Consoles

24. Audio Monitoring on mixing consoles

25. Components of a mixer What it has to offer: Input channels Output channels Monitoring outputs Talk back

26. Input channels Can be either line module (high level) or microphone module (low level). Take Input from the external source. Can be with or without equalizer. Can have stereo inputs with or without remote selectors. Have O/L ,CH ON and ON AIR indications. Have usually 2 auxiliary outputs which can routed independently.

27. Microphone channel • Has the phantom supply to be used with condenser mics. • Has a provision for connecting cough switch for mike muting. • Has microphone input gain control • Has a phase reversal switch. • Has a filter for LF roll off. • Has the provision for panning the signal between left and right outputs.

28. High level input channel • Has input gain control. • Has the provision for panning the signal • between left and right outputs. • Have O/L ,CH ON and ON AIR indications.

29. Output module • Has a gain control. • Has provision for stereo, mono and two independent auxiliary outputs. • Has a compressor/limiter.

30. Mixer setup • The outputs from the mics should not overload the mic preamp inputs. For this, adjust the input gain control of the respective mic channel. • Ensure that, the mix master level is peaking to the 0 dB on the VU meter. • Use talk back facility with the artists for communication. • Ensure that the right level is fed to recorders/amplifiers for clear recording/reproduction.

31. Recording Equipment • Tape Recorders • HDBS system. Here the main factor which affects the quality of recording is the sound card and its level settings and the recording/editing software used. Input level of the sound card depends on many factors like which sound card ,which recording software is being used etc. Level settings become critical in sound card as there is no provision for headroom .

32. Sound cards • A sound card(also known as an audio card) is a computer expansion card that facilitates the input and output of audio signals to/from a computer under control of computer programs. • Many computers have sound capabilities built in, while others require additional expansion cards to provide for audio capability.

33. Standard recording procedure. • Use right microphone meant for that purpose. • Use minimum number of microphones. • When more than one microphone is used ensure that all the corresponding input channel faders are faded in while testing for recording. • Ensure there is no phase out between channels. • Adjustment of proper levels for both input and output channels to avoid overloading. Better maintain the levels marked after alignment by the engineers. • For music programs take sufficient time for balancing the channels. Have a test recording, play it back and satisfy your self. Then you can go in for recording the entire program or live program.

34. Dos and Don’ts of recording • Please do not try to meddle with the levels adjusted in sound card unless you are sure of what you are doing. • Listen to the recorded program, not aux o/p or PFL of input channel etc which may mislead you. • Develop an ear to judge the sound quality of the recorded program. This comes only by practice. No short cuts!!! • Avoid recording your talk yourself without anybody’s help. • Do not record with the microphone placed near the CRT monitors. • Switch the mobile phones off (Not in silent mode) during recording. • Adjustment of proper levels for both input and output channels to avoid overloading. Better maintain the levels marked after alignment by the engineers. • For music programs take sufficient time for balancing the channels. Have a test recording, play it back and satisfy your self. Then you can go in for recording the entire program or live program.

35. DISPLAY OF RECORDED AUDIO

36. A good recording A distorted recording

37. LOUD SPEAKER When an analogue signal passes through the voice coil of the speaker, an electro-magnetic field is produced and whose strength is determined by the current flowing through the coil, which in turn is determined by the volume control setting of the driving amplifier. The electro-magnetic force produced by this field opposes the main magnetic field around it and tries to push the coil in one direction or the other depending upon the interaction between the North and South poles. As the voice coil is permanently attached to the cone/diaphragm this also moves in tandem and its movement causes a disturbance in the air around it thus producing a sound or note. If the input signal is a continuous sine wave then the cone will move in and out acting like a piston pushing and pulling the air as it moves and a continuous single tone will be heard. The strength and therefore its velocity, by which the cone moves produces the loudness of the sound.

38. They are the three components of audio frequencies . • For practical purposes, they can be generally classified as follows: • Low Bass 20 - 80Hz • Mid Bass 80-500Hz • Upper Mid 500-3kHz • Treble 3kHz-20kHz

39. 85 dB SPL 40 Hours   Recommended Monitor Levels For Mixing 90 dB SPL 12 Hours 95 dB SPL 5 Hours Loud Party Level 100 dB SPL 1 Hour High Level Studio Playback 103 dB SPL 30 Minutes Local Bar With Band 109 dB SPL 9 Minutes Bar With Loud Rock Band Best listening Practices • DBSPL: sound pressure level (SPL) produced by one milliwatt (mW) of audio input • While listening, the level you should be monitoring at is 85-90 dBSPL.  Every once in a while it is ok to listen back at 100 dBSPL for a couple of minutes (to check how it sounds at this level) and optimally you should be taking regular breaks.  You should buy a sound level meter to verify the level of the monitoring during sessions. • Hearing loss is a function of sound levels and exposure times.  The louder the sound level, the less exposure time that you can have without sustaining hearing loss.  According to chart published by Etymotic Research (designers of hearing-protection devices), safe exposure to sound levels is shown above.

40. XLR CONNECTORS

41. ¼” stereo and mono jack connections

42. Troubleshooting A Noisy PA System Noise in your P.A. system is a very common, and sometimes a difficult problem to solve. Noise comes from many sources. Some of the most common ones are: 1. Poor cables on the inputs 2. Fluorescent lights 3. Dimmers 4. Poor design, particularly shielding and location of the mixer and power amps power transformers 5. Poor A/C wiring in the location where the P.A. is being used 6. Radio stations or other transmitters in the area 7. Large motors close to the system 8. Grounding problems, when using equipment manufactured by different companies 9. Noise in the input signal, especially guitar pickups. 10. Magnetic fields induced by other nearby components like air conditioners

43. Precautions to be taken • Reduce the length of the cables.  • Wherever possible, use balanced sources • Make sure the input cables are not lying too close to a transformer, motor, amplifier or other source of magnetic radiation • Turn any lights on dimmers off, or if this is not possible, turn them fully on

44. First Reactions  1. Stay calm! Panicking or losing your temper with people or equipment will not make the problem go away.  2. Focus your attention: is the signal reaching its destination? If not, why not?  3. Be methodical. Don't change connections, leads and components at random: work your way along the signal path, eliminating possible causes of failure . If you carry spares (as you should!) you don't need elaborate test equipment: you can always find the culprit by substitution. If a microphone isn't working, replace it with one you know to be OK. If it still doesn't work, replace the cable with one you know to be OK (this also gives you an opportunity to check you have it connected in the right place). Obviously your options are more limited if something happens during the performance - you need to be as inconspicuous as possible - but that means you should be more methodical, not less: don't mute or unplug anything that might interrupt what is happening on stage.  4. Be safe! Electricity kills. Never take the covers off live equipment (always disconnect from the mains before you take the cover off anything. Never replace fuses with any other conductor (wire, nails, screws): if fuses keep blowing, the equipment is faulty and potentially dangerous.   5. Mark faulty equipment. If you find an equipment is faulty, don't just put it back in the bag: mark it in some obvious way (red tape is good for this), put it to one side, and don't take it out with you again until it has been repaired and tested.

45. Emergency Fixes • Failed Microphone. If you have no spares (why not?!), decide whether you can dispense with one: is one of the backline instruments that you would normally mic loud enough to get by? Is the mic on the snare underside essential? Or consolidate existing mics: use a single mic to cover two sources. • Failed Effects Unit. Don't do the song with the timed delay on it (or do it without the delay). The venue probably has enough reverb of its own! • Failed Mixer. Most PA systems with a separate monitor desk (a "spare" in an emergency) travel with experienced crew, who will know what to do. Channel failure is of minor consequence if you have spare channels. If the whole mixer has failed and it is your only mixer, you are in trouble. Your best bet in that case - if you can get away with it - is to let the backline cope as well as it can, while trying to get the main vocals up to a usable level for the power amps. Most of the plastic-box speakers that have built-in power amps will accept mic inputs, so if you are using these you can plug the mic straight into one, and link to any others • Failed Power Amp.  You are in a bit of trouble. Here using microphone along with ampli-speakers will help you to some extend. • Failed Speaker. You may use the spare one if available. In case not, pl re-orient the working ones to cover the audience effectively.

46. Thank You! • Renjith S, • AIR, Mysore. • s_srenjith@yahoo.com