Production Sound Mixer Video Interviews

Underneath all this typing it's sometimes nice to have a few videos to just watch and listen. Some of the rarest to find in the masses and masses of rubbish on youtube are some interviews with sound mixers (there the guys with boom operators) and sound recordists (they do both)


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Heres another great one from Vimeo,

Lossless compared with lossy data compression

When i first looked into this i was like wtf? too... but this is all to do with the data compression.

Lossless data compression is a class of data compression algorithms that allows the exact original data to be reconstructed from the compression data. This is the opposite to lossy data compression, which allows an approximation of the original data to be reconstructed, in exchange fore better compressions rates.

What's the advantages?

One advantage of the lossy methods over lossless methods is that in some cases the lossy method can be compressed smaller than its counterpart, importantly while still meeting the requirements of the application.

Lossy methods are most often used by data are intended for human interpretation where the mind can fill in the blanks or see past minor errors. Ideally lossy compression is transparent or imperceptible, otherwise you would notice it sounded bad and not use it. If you do notice an anomaly it is called a compression artifacts.

Audio can be compressed at 10:1 with imperceptible loss of quality. The compression rate in lossy compression is 5-6%, where as in lossless compression it is about 50-60% of the actual file.

Cheers Guys,

Matt Price

List of Lossy Formats (links to wikipedia)
AAC
ADPCM
ATRAC
Dolby AC-3
MP2
MP3
Musepack (based on Musicam)
Ogg Vorbis (noted for its lack of patent restrictions)
WMA

List of Lossless formats (links to wikipedia)
Free Lossless Audio Codec – FLAC
Apple Lossless – ALAC (Apple Lossless Audio Codec)
apt-X – Lossless
Adaptive Transform Acoustic Coding – ATRAC
Audio Lossless Coding – also known as MPEG-4 ALS
MPEG-4 SLS – also known as HD-AAC
Direct Stream Transfer – DST
Dolby TrueHD
DTS-HD Master Audio
Meridian Lossless Packing – MLP
Monkey's Audio – Monkey's Audio APE
OptimFROG
RealPlayer – RealAudio Lossless
Shorten – SHN
TTA – True Audio Lossless
WavPack – WavPack lossless
WMA Lossless – Windows Media Lossless

PCM - Pulse Code Modulation

PCM or pulse-code modulation is a method to digitally represent sampled analog signals. This is the standard system for digital audio in computers and various DVD, Blu-ray formats and in digital telephone systems.


Each sample is quantized to the nearest value within a range of digital steps. The two properties of PCM are the sample rate and the bit depth, this determines the number of digital values in the range.


See article on Bit depth and Sample Rate for more info.


Cheers,


Matt Price

5.1 Surround Sound, Dolby or DTS?

This is section explaining what Dolby Digital 5.1 and DTS 5.1 are, along with a bit about why people think one is better than the other etc...

What is 5.1?
Refers to this speaker set up: (left front, left rear, right front, right rear, and center), plus a subwoofer channel (the .1 in 5.1)

What is Dolby Digital Surround Sound?
This is the most common format for surround sound on media such as movies. Its a discrete channel surround sound format because the output has been controlled to come from a variety of speakers, allowing a car to sound like it is moving across the screen etc....

What is DTS?
DTS (Digital Theater Systems) is a digital surround-sound system first introduced in theaters in 1993. DVDs encoded with a DTS soundtrack require a DVD player and stereo receiver equipped with DTS-processing capability. This is partly due to the DTS demands for more data space on a DVD (often sacrificing bonus features), but many believe the audio quality to be superior to that of Dolby Digital 5.1-channel surround sound.

What do people think?
I don't happen to be 'the people' but reading up and around the issue DTS has a higher data rate and so that roughly translates into 'better' sound. Where as many Dolby fans argue that low compression but higher data rate provides 'better sound'....

Ill need another 10 years to provide a better description of 'better sound' but many blogs start with the underdog against the giant, like in all fairy tales...

I should be pointed out that both Dolby Digital and DTS Digital Surround encoding schemes now have even higher sampling rate of 48 kHz at 20-bits per sample, thus yielding an even wider dynamic range between sound level extremes of approximately 120dB.

They both have to be compressed in some form to fit on the disk so that is always going to be an issue, raw data over efficiency is hard to prove when sound is subjective.

"Compression and bit-rate are not the only differences when comparing Dolby vs. DTS formats. For example, the added rear surround channel in Dolby's extended surround format 'Dolby Digital EX', is matrixed over the two left and right surrounds, rather than discrete; instead the DTS counterpart uses a discrete channel. This also explains why DTS ES (Extended Surround) can provide a more precise location for the rear-effects soundstage than the Dolby EX format." - Source here

"Both Dolby Digital and DTS audio are capable of achieving similar end results in delivering surround sound, even though the lower compression/higher bit-rate of DTS Digital Surround should theoretically yields apparent benefits in sound quality.

At the same time, one cannot ignore the fact that these two formats make use of different coding schemes and syntax to perceptually compress audio.

This means that efficiency in terms of data utilization between these two formats is different. Therefore, a Dolby vs. DTS direct comparison based solely on these formats raw bit rates cannot be taken as a measure of sound-quality.

Thus, while it is objectively possible to compare the resultant sound quality for the same audio format encoded at different bit rates, and therefore, to determine whether the same format in a moviehouse application sounds better or worse than in a consumer implementation in home entertainment, it is not so straightforward when dealing with different formats.

Rather, the reality is that for identically sourced audio content, it would be much easier for the listener during a Dolby vs. DTS 'blind' listening test to notice a change in sound quality when changing the playback equipment say between different brands, than when changing from a Dolby Digital to the DTS surround audio track." - Source here

So it is down to choice really and if it you set up your theatre, home cinema etc... then you might notice one suiting your needs better, Sadly this is going to be a never ending debate but at least you can argue both ways forever with your friends.

Thanks

Matt Price

Sampling theorem

The Nyquist–Shannon sampling theorem, after Harry Nyquist and Claude Shannon, is a fundamental result in the field of information theory, in particular telecommunications and signal processing. Sampling is the process of converting a signal(for example, a function of continuous time or space) into a numeric sequence (a function of discrete time or space).

Sampling theorem which in essence shows that a bandlimited analog signal can be reconstructed perfectly from an infinite sequence of samples if the sample rate exceeds 2B samples per second. B is the highest frequency in the original signal. If the signal contains components at exactly B hertz, then samples spaced 1/(2B) seconds do NOT completely determine the signal.

E.g. 20,000 Hertz into this forumla will not be reconstructed perfectly at anything less than 0.00003 seconds per sample. Recording at a sample rate of 48kHz is sampling at 0.00002 seconds per sample, hence for situations like recording dialogue where the highest frequency for normal conversation is below 20kHz (because we can't hear higher).

Possibly Useful Drawing of a 2hz sine wave

So in recording effects if you wanted to have flexibility to manipulate then you can record at 192kHz and then the spacing is 1 sample every 0.0000052083 of a second, this is useful for slowing down samples more effectively than less samples.

This is again like most perfect theories based on a perfect world and so is an approximate in our not so perfect world.

Hope this ended up making sense.

Thanks,

Matt Price

The famous Wilhelm scream

The Wilhelm Scream originates from the film Distant Drums in 1951. The scene in the video below soliders are wading through a swamp and one (Wilhelm) gets bitted and dragged underwater by an aligator, the scream was re-recorded in a single take, along with 5 others. the 4th 5th and 6th are also used earlier in the movie. 4-6 are all recognisable as the Wilhelm scream by many sound editors.

Below is the scene with the original Wilhelm Scream.

Below is a compalation of Wilhelm screams

Hope you enjoyed this,
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

Q+A: 6 Miscellaneous Sound Questions... Part 1

Compilation of general and random questions...

1. What does 94.1 mean on a radio dial?

This mean the station is emitting at 94.1 million Hertz or 94,100,000 waves per second.

2. If sound becomes louder, what wave characteristics increase? frequency, wavelength, amplitude or speed?

Only amplitude.

3. How much bigger is a sound at 40dB compared to 0dB? 

10,000 times.

4. How much bigger is a sound at 110dB compared to 50dB?

1,000,000 times.

5. What does supersonic mean? 

Faster than the speed of sound

6. General speeds according to (this site)

WATER:
Distilled water = 1489 m/sec
Sea Water = 1531 m/sec (higher because it is denser)
WOOD:
Ash, along the fiber = 4670 m/sec
Ash, across the rings = 1390 m/sec, about 3 times slower, and a little slower
than the speed of water!
Beech, along the fiber = 3340 m/sec
Elm, along the fiber = 4120 m/sec
Maple, along the fiber = 4110 m/sec
Oak, along the fiber = 3950 m/sec.


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

The camera that changed the world

Film Link: Camera That Changed the World
Only available for the next 5 days.


This is a quick post about a documentary availible on the BBC iPlayer that shows the evolution of the portable camera and how important it was to the documentary genre. At around the 45 minuite mark there is a short section on the importance of the Nagra and sync sound. So if you can spare an hour over the next 5 days it's worth a watch.


Thanks,


Matt Price