T351 Week 2 - Summer 2008

Agenda:

• Continuity & audio
• Review Art Video & Interview/Feature Proposals (Due Tues)
• Carry out Audio / News Exercise
• Final Project ideas (Thursday)

Announcements/Reality Check:

• Label your tapes and boxes on the spine!
• Exposure: If you are having a hard time- start by looking at color bars. to make sure your viewfinder is adjusted properly. THen see what the camera thinks the exposure should be (auto-iris).
• Did you finish the Week 1 readings? It's time for Week 2 (sound).
• Lecture today - Cover continuity & audio. Turn in Art Video Pre-production materials. (You may start shooting these anytime after you turn in your pre-production work.)
• Lab Tuesday - Review Storyboard Exercises. Carry out Graphics Lab & Graphics Assignment (10 points). Review Interview / Feature Story proposals. Pair students up for Drama/Storytelling Exercise & as production pals. Carry out Audio / News Exercise.
• Lab Wed - Carry out Audio / News Exercise. Try to log/capture your footage before
• Lab Thursday - This class time is dedicated for you to edit your Audio / News Exercises. These should be finished by 3 PM Thursday!
• Next week we'll cover lighting & you'll shoot your interview/feature stories.

Misc/Useful Information:

• Jim's Graphic Tips
• Jim's Timecode info

SOUND - (Readings: Cybercollege units 37, 38, 39 & 40)

Components

• Introduction
• Loudness & Frequency
• Types of microphones and their application
• Signals & metering
• Examples (music, close up miking, long shot miking, ambience etc)
• Lab assignment:

Introduction

Audio for film and video is more than just recording a good signal. Most soundtracks are multi-layered creations that go far beyond providing us with dialogue from our performers. We hear cues that tell us where they are- outside, inside, who’s sitting on the left or right, how big the room or environment is. How many people are milling about in the background and what they are doing? Maybe what the weather is like.

You could place two people at a table in a restaurant set and record pristine audio with a $2,000 microphone. It might sound great, but it’s not going to fly with a TV audience. It would sound weird. Viewers expect to hear clinking silverware, the murmur of other diners and music playing over the sound system. A classy restaurant on Friday night would sound much different than a diner on Saturday morning.

If you need backgrounds or sound effects for your production you have a few choices. The production lab has a sound effects library that we share with WTIU. You can also record background sounds yourself with the camera (it does have digital audio).

We'll cover specific tips and techniques in lab.

Stereo imaging & perspective

More and more people have surround sound systems or at least listen to their TVs in stereo. The audio playback you have at home is probably better than what we have through the G4s.

Viewers expect audio from people on the left side of the frame in a long shot to come from the left side speaker in their TV sound systems. Take a two shot of our couple at a table in the restaurant. The audio from the person on the left comes from the left side speaker. But then we cut in to a full screen close up. The sound then comes from the middle. To further complicate things, we (sophisticated viewers with surround sound systems) are used to having the audio perspective match the camera perspective. At a long shot in the restaurant we expect to hear more room noise- more diners and waiters walking by. Think about the production logistics involved in this. Then we cut in to the two shot. It sounds closer. We cut in to the close-up. It sounds closer still.

This is why the boom mike is sometimes favored over lavalieres for recording dialog. We can easily vary the distance so the audio perspective matches the camera perspective.

Loudness & Frequency

Loudness can be measured in decibels (dBs) and be represented visually with VU meters.

Metering & Level Setting: Analog vs. Digital

The scale on a VU meter goes from –20 db to +3. We set the levels so most sounds are underneath 0 with the peaks going up into the red area.

Common practice is to use a 1 kHz tone at 0 on the VU meter for reference purposes. For example we always record color bars at the beginning of tape. It should be accompanied with 1 kHz tone at 0 VU.

In digital audio, there is absolutely no headroom over 0. So to avoid the signal becoming clipped, we must set our reference tone somewhere below 0. How far below 0? Well it depends on a number of things, namely how much headroom you'd like to keep. There are several accepted levels for setting the standard, 1 kHz reference tone: These include –20, -18 (most common) but -14 is also used.

Just because a meter is digital doesn’t mean it’s for digital audio. Look at the numbering scale to determine if it’s for digital or analog audio.

AGC

Automatic gain control circuits try to get a consistent level. If it’s soft, it’ll boost the signal. If it’s loud it’ll turn it down. Don’t use it! It’ll bring the noise floor up and reduce your dynamic range.

Frequency is measured in Hertz or cycles per second

• Hertz = CPS cycles per second
• Kilohertz (kHz) = 1000 Hertz
• Human hearing generally ranges from 20 Hz to 20 kHz
• Concert A = 440 Hz
• Middle C is 261.63 Hz
• The human voice ranges from about 100 – 9,000 Hz

Microphones

Microphones convert one form of energy to another: sound waves to electric energy

Microphones can be classified by their electrical characteristics and pickup patterns.

Electrical Characteristics:

Dynamic - Works opposite of a speaker. A wire coil attached to a diaphragm is suspended inside a magnetic field. Sound waves hit the diaphragm making the coil move. This creates a flow of electricity in the coil windings.
Dynamic microphones are typically durable and a good choice for hand held vocals or percussion instruments.

Condenser - (a.k.a. electret or capacitor)- Need batteries or phantom power to operate. A plate or diaphragm moves adjacent to a stationary, charged backplate. The capacitance between the two plates changes as the diaphragm moves modulating an electric current. This current must be boosted by a preamplifier to create a usable signal.

Condenser microphones are more sensitive and create a “hotter” signal. They are a better choice for distant miking and lower level sound sources. Most full range, high-quality studio microphones are condensers.
You must either use batteries or phantom power. Phantom power is 48 volts, which is sent up the microphone cable from the mixer or camera. (Most professional cameras – like the JVCs have phantom power)

Ribbon - A small (extremely delicate) metal ribbon is suspended inside a magnetic field. Sound waves move the ribbon, creating an electrical flow. Because of their delicate construction, ribbon microphones are not suitable for windy conditions or extremely loud sound sources. They are typically only used for vocal applications. (The RCA mike on Johnny Carson’s desk was a ribbon microphone)

Pickup patterns:

Omni (EV635 is the most commonly found dynamic mike. Most lavaliere microphones are condensers and have omni-directional pickup patterns)

Cardioid (dynamic cardioids include SM57 SM58 & the RE20. Condenser cardioids include AKGC100, AT4033)

Hyper-cardioid (Shotgun microphones- almost all are condensers)

Figure eight (All ribbon microphones. The U87 & AKG414 are switchable between Cardioid and figure eight)

Other (boundary or PZM, contact etc)

Boundary or Pressure Zone Microphones (PZM) are flat and designed to be placed on a flat surface. Their pickup pattern resembles half of a sphere.

Contact microphones are small and designed to be mounted directly onto a resonating object. (Onto the bridge of a cello or the inside of a guitar) These are used mostly for music.

Applications:

Lavaliere (wireless are the norm) Very popular for film & video. Provide a consistent sound close to the source and are inconspicuous. Wireless versions of these are a must have for professional videographers.

Hand held – try to avoid using these unless you’re doing interviews with people on the street (an assistant with a boom would be better). When using, make sure to keep them a consistent distance from the source. Best used on a stand.

Stands (floor & desk) obtrusive good for music; desk: obtrusive but an excellent way to hold a microphone (Leno, Letterman)

Boom – handheld and floor stand models (typically used with a shotgun mike)

Headset – Conspicuous but provide audio monitoring for performers and a consistent sound source. (Used frequently for live sporting events and by singers)

Parabolic mount. A large bowl with handle on the outside and a microphone mount on the inside. Place a microphone in the middle and you have a highly directional microphone- more directional and sensitive than a shotgun mike. Commonly used for sporting events and spying, be sure you faithfully listen to the headphone while using. You need to move these continuously to keep them focused.

Signals, cables and connectors

Mic / Line Level - Audio signals are typically either line level or mike level.

Different line levels (+4 dBm & –10 dBm). There are two different levels considered "line level". Professional equipment uses a slightly hotter signal of +4 dBm. Consumer equipment (such as CD players, VCRs, etc) uses -10 dBm. They are usually interchangeable, but plugging a +4 output into a -10 dBm input will sound louder and possibly clip or distort. Plugging a -10 dBm output from a piece of consumer gear into the +4 input of a mixer will usually work fine, except the signal might be slightly softer.

Balanced vs. Unbalanced - Audio cables are either balanced or unbalanced

Balanced cables have three wires (two conductors & a ground) and are far less prone to electrical interference than unbalanced (2-wire) cables. Long cable runs of unbalanced cables will also cause a loss in high frequencies.

The cables that connect your home stereo equipment together (with RCA connectors on the ends) are unbalanced lines. They only have two wires, a conductor and a ground. The cables with XLR connectors on the ends (like mike cables) are balanced. They have three wires- two conductors and a ground- that’s why they have three pins or plugs on the connectors.

Balanced lines are less likely to pick up hum and distortion than unbalanced lines. You can use them on long cable runs without audio degradation. Unbalanced lines are likely to pick up radio interference and lose high frequencies on long cable runs.

Running cables - Don't run cables adjacent to AC power cords. Keep them separated as much as possible and cross them at 90 at intersections.

Learn to wrap cables! You need this to work professionally- really. Will cover in lab.

Wireless microphones - Diversity vs. Non-Diversity - Diversity receivers have two antennas.

Compressors - Used to reduce the dynamic range (loudness). Digital audio has a great deal of dynamic range (signal to noise). Unfortunately we often need to reduce the amount of dynamic range to make the audio signal more suitable for analog tape, TV broadcast or for radio transmission.

Compressors let you select a threshold level. Sounds louder than the threshold are compressed by an amount that you can specify. You can also set the attack and delay of the compression.

Audio that has been compressed sounds louder than non-compressed audio. Reducing the overall dynamic range creates less variation in the signal. In other words, the difference between the loud and soft portion is reduced. With a more consistent audio level, the overall signal gain can be increased.

Limiters - They reduce the dynamic range (like compressors), but can totally limit the signal, not just reduce it.

Expanders - The opposite of a compressor. Sounds above a set threshold are expanded, or the gain is increased.

TIPS

• Never use AGC, unless you are in an extreme situation and really don't have time to mess with the audio (covering a fire
• When recording audio always record two tracks- one for the source (talent) the other for the environment. (In a pinch the camera mike will do for the ambient mike)
• On location for interviews & dialog? Always record some ambient audio with a high-quality microphone. This can be layered into the soundtrack during post. If you need to add some dialog to a scene, you’ll have a background bed to lay under it.
• When scouting shooting locations listen. Is it quiet enough? (vehicle noise, construction)
• Faithfully monitor your audio with headphone while shooting. Listen to both tracks. Record a little and play it back. If you are in a noisy environment, go to somewhere you can hear it.
• Make sure you don’t record any copyrighted music in the background.
  Use the same microphone for your voice-overs as for the on-camera.

Microphone techniques

How would you record an on-camera announcer?
With a guest?
Three people at a table?
A scene with action & movement?

 

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