5 More Pre Production Location Sound Recording Basics (Part 2)

As I am a generious guy I thought I would bash out part 2 of pre production basics (meaning essencials and at the very least)
read part one of 5 pre production basics part one

6. Double system 99% of the time
Unless this is a run and gun documentry or live broadcast location news then you probably have the freedom to easily slate and thus easily sync sound from a seperate sound recording device. The double system gets its name because you have one system for visuals and one for sound (according to my understanding)
This has many advantages such as easier capture for wildtracks, better quality recording due to higher quality specific sound recording electronics and wiring, more flexability to be out of the cameras way and less interference from longer cables, balanced or otherwise.

7. Order of priority
Equipment wise, your only as good as your weakest link and many other metephors a side, the equipment is of this importance as it works in a chain, obviously if anything in this chain is terrible then bring that up to the level of the others.
Your first link is the microphone/s its self, this will determine the amount of electronic current that needs amplifaction, the quality of the frequency response and how much other sound outside the polar pattern will be discrete (blocked).
Next is the mixer of some sort (please not just your camera!) Where it will be able to amplify the microphones electric voltage differences to acoustic energy and the better the pre amps and limiters the better the signal to noise ratio and the less your likley to peak and distort any unwanted, un expexted loud sounds.
Finally the recording device which is last because thankfully you have a good mixer doing most the leg work, dont you :-), this allows the freedome of the double system mentioned earlier.
Also dont forget to get balanced cables (refer to glossary) and the fewer cable to cable connections the lesser the chance of interference and noise being amplified with any recording. along with a good support for your microphone on a boom pole so you limit handling noise.

8. Information is only potencial power
Grab as much information on storyboards and floor plans and sizes of rooms and whats near by the location referring to the script. This could save you loads of time on the day in regards to descision making and mike placement, we both know its never exactly like the plan but better to have a guide!

9. Be ahead of the game
Referring to the edit, before hand you can draw up lists for wildtracks and sound effects which could be benificial to the troops in the edit. On another small note: REMEMBER ROOM TONE/ATMOSPHERE RECORDINGS FOR EVERY LOCATION. It's kind of useful, do at least 15 clean! seconds

Finally Number 10. Fail to plan, plan to fail
Not all these elements might be relevant to the situation but it does save you time in the long run and sets a good solid foundation for the edit. After we are part of a bigger creative team to achieve a great end result and just by reading articles like this you know it's more than a job but a lifestyle especially in independant low budget projects. :-) happy days.

Thanks.and comment or share below

Matt Price

Phase and Interference...

What is wave interference?
when two or more waves from different sources are present at the same time in the same space to create a new wave. The more useful part of this question is what happens and what types there are...
Constructive Interference
when the compressions and the rarefactions match they create a wave of higher intensity.
Destructive Interference
When the waves are out of phase, as in the opposite to constructive interference but the sound is louder in some places and softer in other places. Often leading to pulses and beats of sound.
What is a Phase?
Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.
What is Phasing?
The relationship between the waves to form the new wave, often used to describe the resulting sound, commonly constructive or destructive.
Dead Spots?
This is where the compression of one wave matches or is in phase with the rarefaction of another and so the sound is cancelled out and nothing is heard.
What else to consider?
Sound waves also change speed due to rarefaction from entering different mediums such as air to water, thus changing angle and bending the wave. this leads onto:
The critical angle..
When a waves entering angle reaches a certain point it's called the critical angle. The rarefaction is parallel to the dividing line between the mediums. The greater the difference in speed from the sound in the two mediums, the greater the critical angle.
What does this mean?
If the sound hits the new medium with any angle smaller then the critical angle it will not be able to enter and so be reflected from the dividing line. Even if it enters the medium some will be reflected because of waves rarely propagate in straight lines only.
Example...
A wave travelling through the air hits a building at 20 degrees, which for this example is less than the critical angle, then it is all reflected at 160 degrees as the total angle is 180 degrees of the wall.
If the wave is above the critical angle then most will enter the brick and speed up because the molecules are closer and so is refracted. The rest bouncing off because it won't all be entering with in the critical angle. 

Hope this all flowed nicely,
Thanks,
Matt Price

Refraction

This is the bending of waves when they enter a medium where their speed is different. This is less important than refraction of light as it affects image formation of images by lenses and eyes etc... 

If we use the example illustrated above shows that the first medium of air the light travels straight but when it hits the second medium of the glass it bends depending on which side hits the second medium first, it will bend left if the left side hits the second medium and slows down and refracts. 


Not only the direction changes but separation of the waves decreases as the frequency of the waves does not change by its source but the shower speed must shorten the wavelength.


This is also interesting in sound because if the air above the earth is warmer than the surface, sound will bend back downwards towards the surface by refraction. If the air above the earth is warmer than that at the surface, sound will be bent back downward toward the surface by refraction.


Refraction also amplifies sound sometimes over cool lakes in the morning. The water keeps the air cool near the water but as the sun comes up it heats the air higher up creating a thermal inversion. The speed of sound is faster in the warmer air and so bends some sound back towards you.


also see: Diffraction


Thanks,


Matt Price

Diffraction

One of the interesting properties of sound waves is that they can diffract like the image below demonstrates.

The possibility of hearing around corners or barriers involves diffraction and reflection of sound. Diffraction is mostly associated with longer wave lengths as thus implies that you hear low frequencies than higher ones. This is also explained by the fact air absorbs higher frequencies better than lower ones. A lightning strike for instance has a high crackle with a longer low rumble.

Sound proofing rooms takes this into account and so the room has to be fully sealed because diffraction can disrupt a lot from the smallest gaps. This is a similar reason for loud speakers to be sealed so they maximise output. 

An interesting characteristic involving imaging. When a wavelength is longer than an obstacle, for instance a pillar means you can't see the obstacle. This is the same reason you cant see a virus under a light microscope because the virus is smaller than the waves of light. This is due to the bigger wavelength diffracting round the obstacle and reconstructing past it. 

See also: Refraction

Feel free to comment,

Thanks,

Matt Price

Reverberation Time

A reverberant sound in any closed space like a room or concert hall diminishes as the sound energy is absorbed by multiple interactions with the surfaces of the room. Though the speed it takes to diminish depends on the variable of the rooms surfaces, for instance a reflective  or "live" room will take longer than a very absorbent or "dead" room. The time for the sound to completely die away will depend how loud the sound is at the start and how well the observer hears. 


The standard reverberation time has be established as the time it takes for a sound source to diminish by 60 dB below its original level. This is established at 60dB from testing in auditoriums where the loudest crescendo in an orchestra is 100dB and typical background noise for a music-making area being around 40dB. 60dB is also roughly the dynamic range for orchestral music.


In terms of time it depends on the rooms use. In a classroom you want the room to have low reverberation time to keep articulation clear and reduce build up from people talking. In an auditorium you probably want a bit more so you can really feel the music. As a general rule you wont get long reverberation time in a small room because of how fast the energy is bouncing off the surfaces and being absorbed a bit each time.


Reverberation time is just one part in creating pleasing environments for sound, you also need to consider the absorption in terms of frequencies.


Thanks,


Matt Price

Inverse Square Law Of Sound

Hello All,


This blog is on the inverse square law of sound which is a very important law that not many really know about (we will get onto that later) Sound waves propagate spherically and so distributed over and ever increasing surface of diameter at the front surface of the wave. The inverse square law tells us that every doubling of the distance from the sound source in a free field situation the sound pressure level will diminish by 6 decibels.


Why many may not know this law is that it is hard to get a free field situation such as an explosion of a bomb in mid air. Though not perfect for real life situations it is a very important guide to sound sources and how they diminish over distance. 


As an example lets say a person shouts at 70dB at 3 feet away from you in a room, at 6 feet it will be 62dB and at 12 feet 56dB and at 24 feet 50dB. This example on works as a guide not taking into account reflections from any walls of a room and any other sound in the room at the time of shouting.


Thanks,


Matt Price

World-a-lies-ing

Instead of you having to read everything like back in the 1800's i thought i would indulge all your senses to a quick video interview with Walter Murch. I will write up another blog that will go into more detail about different types of reflections of sound off surfaces and all of that jazz later today as i have just a few more days till im back on several shoots. Enjoy!

Manipulating sound until it seemed to be something that existed in real space. This refers to playing back existing recordings through a speaker or speakers in real-world acoustic situations, and recording that playback with microphones so that the new recording takes on the acoustic characteristics of the place it was "re-recorded." [via filmsound.org]

Thanks,

Matt Price