stereo and surround mixing techniques

Stereo and Surround Mixing Techniques

Mixing Techniques Broadcast Vs. Theatrical

The most significant difference between home and theatrical mixes is the dynamic content of the mix.

Mixing for home viewing sometimes involves making compromises in order to ensure that the mix translates to the maximum amount of end users.

Primarily this involves raising the low parts so that they won’t be lost in the high noise floor environment typically found in the home.

Mixing Techniques Broadcast Vs. Theatrical

Much of the detail work in dialogue editing is also more apparent in the home environment due to 2 reasons.

- Audience’s proximity to the speakers

- No screen between the speakers and the audience

Mixing Techniques Broadcast Vs. Theatrical

Delivery specs also differ between the 2, and different tools are needed for to accomplish them for each.

A few typical television specs might be

-Content should be mixed in a properly calibrated -room

-Peak audio at -10dbfs

-Dialogue at -24lkfs +/-2db

-Overall Levels at -24lkfs +/-2db

-Average levels hovering around -20dbfs

Mixing Techniques Broadcast Metering

The Dolby Media Meter allows the engineer to monitor lkfs levels which are becoming the de-facto spec for broadcasters.

The TC Electronic LM5 is also a viable option.

Broadcast engineers often use Dorrough meters as well. These allow the engineer to monitor both peak level and average loudness

Many “old school” engineers still like the feel of traditional vu meters and use them as a reference though the dbv spec has virtually disappeared.

Mixing Techniques Theatrical Trailer or Commercial

-Content must be mixed in a properly calibrated studio

-No peak measurement

-Loudness must not break 86 Leq(m)

The Dolby Media Meter is capable of measuring Leq(m), but at some point the audio will need to pass through Dolby’s DMU for mastering and encoding which also measures Leq(m)

Mixing Techniques Broadcast Vs. Theatrical

Film for Theatrical Release

-Content must be mixed in a properly calibrated studio

-There are no peak, average or Loudness measurements

-Mixes are done to ear and then typically mastered on -the Dolby DMU (for Dolby Print Mastering)

-The DMU also provides metering

Mixing Techniques Loudness

The hot topic of the moment in audio post seems to be the idea of loudness, and its perception.

The Leq measurement is designed to measure loudness over time.

Basically the measurements we discuss are based on this concept. Each variation applies a different filter to their loudness measurement and therefore yield different results.

Mixing Techniques Loudness

Leq(m) for example is designed to be sensitive to the mid and high frequencies that audiences in theatres might find objectionable at high volumes.

Lkfs is the current loudness standard for television and stands for Loudness K-weighted relative to Full Scale. This is often measured with dialogue intelligence on which allows the meter to measure only the dialogue loudness and gives the mixer the ability to add dynamics through the other elements.

Mixing Techniques Loudness

The CALM act was passed in on September 29th, 2010, and mandates the maximum loudness in commercials not exceed the average maximum loudness of the accompanying programming.

The FCC must enforce this law within a year of its passing.

Mixing Techniques Calibration

The process for calibrating a studio for theatrical mixing and television mixing are similar.

Pink noise is used to calibrate SPL at the mix position.

For theatrical mixing pink noise ins generated from the mixing platform (pro tools) at -20dbfs and output through one speaker at a time. Each speaker is adjusted to read 85 dbspl at the mix position.

Mixing Techniques Calibration

For broadcast mixing, pink noise is generated from the mixing platform (pro tools) at -20dbfs as well. In this situation each speaker is adjusted to read 79 dbspl at the mix position.

What is the result of mixing on lower volume levels?

Mixing Techniques Calibration

Studio size is also a concern.

It is recommended that you lower the dbspl reading at the mix position as the proximity between the speakers and the mix position increases.

So for smaller studios, films are recommended to be calibrated at 79 db, and as low as 76 for broadcast.

Mixing Techniques Calibration

The reason for this change is the psycho-acoustic effect speaker proximity and room size has on the way we perceive loudness.

Our perception of loudness increases as we get closer to a sound source and as the space in which the sound is perceived decreases.

Mixing Techniques Subwoofer Calibration

Subwoofer calibration is a bit more murky and depends largely on your specific system configuration.

In general the same rules apply to the sub as the main channels. Some documents require filtered noise to be sent to the sub and then measured, some require alignment 3-6db lower than the other channels.

In theatrical applications a Real Time Analyzer is often used to get a specific view of the frequency readings.

Mixing Techniques Subwoofer Calibration

Consumer subwoofer setups very greatly and knowledge of the concept of bass management and its principles is important in order to create a good 5.1 mix.

Mixing Techniques Starting the Mix

The session template is opened that is most appropriate. Many engineers have one template capable of handling numerous tasks.

As illustrated in the setup class the first step is loading the OMF/AAF file.

Mixing Techniques Starting the Mix

This file should load with proper handles in order to facilitate the mixing process.

Handles allow each audio file to be trimmed out an additional pre-determined amount of time.

For longer form projects sometimes handles up to 10 seconds are considered standard, whereas for short form, many times 2 second handles are sufficient.

Increasing handle size will increase the file size of your OMF/AAF.

Mixing Techniques Starting the Mix

In order to ensure that all files are properly aligned it is considered standard practice for the first frame of video to start at 1 hour.

The omf/aaf file should load so that the first frame of audio begins at 01:00:00;00.

Many times video editors will add an arbitrary number of black frames at the head of the video file.

The only way to ensure proper alignment is to load the audio from the quicktime and line the audio from the video up to the audio from the OMF/AAF

Mixing Techniques Starting the Mix

The most foolproof method is to have the editor add a 2 pop in the omf that corresponds to a flash from on the video.

The 2 pop is typically a 1 or 2 frame 1khz pop that starts exactly 2 seconds before the first frame of video. By aligning the pop with the flash frame we can assure proper sync.

Broadcast wave files also allow for time stamping which can be useful for both sound engineers and video editors as the time code location is embedded in the audio file as a form of metadata.

Mixing Techniques Stem Mixing

Once the initial editing phase of each stem is under-way the pre-mix process begins.

Level, eq, compression and noise reduction choices are made.

Ideally we want our pre-mixes to have as little compression as possible but still feel controlled.

Certain stems are capable of handling more compression than others.

The music stem tends to have less compression as a whole whereas the effects stem may be more compressed.

In the end these are creative decisions that will define the sound of the mix and will have to be made on a case by case basis.

Mixing Techniques Mixing

If the project has had a number of people working simultaneously on the different stems we must now bring the elements together and find a way for them to inhabit the same soundtrack.

Maintaining eq and dynamic control is the main way this is achieved.

Mixing Techniques Mixing

As we bring together these element we start to notice the limitations of certain systems particularly while mixing in 5.1.

Decisions will have to be made about bussing architecture and processing in order to maximize our systems.

Changing playback engine settings can often buy you more dsp from the system.