T351 Week 5 - Spring 2008

Agenda:

• Cover audio - will maybe get started with some lighting.
• Discuss Audio / News Exercise (THIS WEEK IN LAB- be sure to view the on-line assignment details before lab this week.) You must bring two copies

Announcements/Reality check:

• Lab this week: Audio / news exercise - Be sure to come to lab prepared with the appropriate paperwork! (See details near the bottom of this page)
• Bring in proposal/topic for Interview / Feature story. Paperwork will be due the following week.
• We'll spend about one hour on editing and sharing interview topics- then send you out in groups to do the exercise.
• Next week we'll cover lighting and have a demo in lecture. In lab you'lll carry out an interview/lighting setup. The week after you'll shoot the Interview / Feature story assignment .
• You should also be formulating your art project. The proposal isn't due for two weeks- but now is a good time to plan.

SOUND

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. Audio is an important tool used to motivate edits. (Cutting to the beat in a music video for example.)

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 speakers on our editing computers or inexpensive headphones. Because of this it's important to ensure the sound is well-produced.

Viewers expect sounds from far away to sound more distant and sounds nearby to sound more present. We've been listening to stereo and surround audio for years and are acutomed to taking cues of character positions or locations through the soundtrack. Imagine a long shot in a busy restaurant as our two stars enter and sit down at a table. Over the long shot we'd expect to hear quite a bit of ambient sounds. But then we cut into a closeer two shot, and the audio must sound more intimate. In addition there's stereo imaging. The audio from the person on the left comes from the left side speaker. But then we cut in to the character with a full screen close up. The sound then comes from the middle.

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.

Digital meters are different. The scale starts at around -50 and goes up to 0. In digital audio, there is absolutely no headroom over 0. S 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, and -14.

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

• In general, shotgun mikes on stands or boom poles, or lavaliere mikes work great for interviews.
• Never use AGC unless you have no other option (shooting breaking news, covering a fire, etc.). If you do, use one channel set for AGC and the other on manual.
• When shooting B-roll or any video, always record audio- even if you don't think you are going to use it.
• When shooting interviews you can use one track for your subject and the other for either your interviewer or just NAT sound from the camera. (Sometime I record the subject with two mic- a lav AND a shotgun mounted on a stand outside of the frame.)
• On location, always record some ambient audio with the same microphone you are recording your interview with. (Often called room tone.) 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 closed ear headphones while shooting. Listen to both tracks. Listen for drop-outs, popped Ps or Ts, and any other distortion. Record a little and play it back. If you are in a noisy environment, go to somewhere where 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

Setups to ponder. How would you record the following:

• An on-camera news announcer? (In the field? Anchoring behind a desk?)
• An interviewer with a guest?
• Three people having a roundtable discussion at a table?
• A dramatic scene in a house with lots of action & movement?

There is no single "right" way to do any of them. What you choose will depend upon your level of skill and available equipment. The Telecom Dept does have stands, additional microphones and field mixers you can check out.

Lab this week:

You will carry out the Audio / News Exercise. Be sure to bring two copies of your paperwork. You'll also need to get either on-camera releases, or use paper releases (found on the website.)

Artistic Expressions Video - Please begin thinking about and planning this. Initial deas are due next week. The official proposal is due shortly thereafter. Now is the time to plan. Be sure you know the criteria for the assignment.

Interview / Feature Story projects:

We share ideas in lab this week! You will need to lock into your project and submit your pre-production work next week. We will assign partners and times next week in lab. Be sure to check out the criteria for the asisgnment. Scheduling: Remember you should try to shoot this project in lab if at all possible. If you and your partner are shooting two different interviews, you could schedule one at 9 and the other at 11.

 

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