Upmixing

An overview and explanation of the upmixing controls.

UPMAX ISC uses the latest Linear Acoustic® upmixing algorithm for upmixing from 2-, 3-, 5.1-, and 7.1-channel audio to immersive formats including 5.1.2, 5.1.4 and 7.1.2. If the channel count and format of the incoming content matches the desired output format, UPMAX ISC will pass it through as-is.

The UPMAX menu is separated into Basic and Advanced sections. The Basic menu is displayed by default. The Advanced menu can be expanded with a dropdown menu as needed.

The controls in the Basic menu can be divided into four basic groups: Format controls (6-1A), LFE Channel controls (6-1B), Center Width controls (6-1C), and Auto-Detect controls (6-1D).

Format Controls

Input Format

The Input Format menu (6-2A) is used to specify the channel format of the source audio. If the input format matches the selected output format (as selected with the Output Format control) the unit will pass the signal through as-is without additional processing. Input options include:

Auto Detect: In this mode, the unit continuously monitors the input signal to determine its format and will automatically switch to one of the processing modes below (Stereo, Stereo + Dialog, or 5.1)
Stereo: Stereo content will be upmixed to the desired output format
Stereo + Dialog: Stereo content will be upmixed to the desired output format, while a dedicated dialog input on Channel 3 will be passed through to the Center output
5.1: 5-1-channel content will be upmixed to the desired output format
Pass-through: Pass-through will pass the input signal directly through to the output with no additional processing; this can be used as a “soft bypass” function as the signal still runs through the upmixer and therefore incurs the same amount of latency as it would if it was actually upmixing a signal, thereby preserving A/V sync and avoiding lip-sync issues

When Auto Detect is selected, enabling the Center Detect control (6-2B) upmixes stereo content to the specified output format but ignores the presence of audio on Channel 3, which is typically dialog. The Channel 3 audio is time-aligned and summed with the upmixed version of the audio at the output. This is especially useful in sports production where announcer dialog is often routed on a separate bus, giving downstream facilities the options to edit or replace the announcer track.

Output Format

The Output Format menu (6-2C) determines the output channel configuration. Output options include:

5.1: Provides a constant 5.1-channel output from Stereo, Stereo + Dialog, and 5.1-channel input sources
5.1 Legacy: Like the standard 5.1 output, it provides a constant 5.1-channel output from Stereo, Stereo + Dialog, and 5.1-channel input sources but with upmixing that is sonically closer to the previous UPMAX algorithm used in the Linear Acoustic UPMAX v4 upmixer and the algorithm employed in the various Linear Acoustic AERO®-series processors
7.1: Provides a constant 7.1-channel output from Stereo, Stereo + Dialog, 5.1-channel, and 7.1-channel input sources
7.1+2: Provides a constant 7.1.2-channel output from Stereo, Stereo + Dialog, 5.1-channel, 7.1-channel, or 7.1.2-channel input sources
5.1+4: Provides a constant 5.1.4-channel output from Stereo, Stereo + Dialog, 5.1-channel, or 5.1.4-channel input sources

LFE Channel Controls

The LFE channel controls are used to tune the crossover frequencies, gain, and signal routing of the low- frequency effects audio.

LFE Crossover

The LFE Crossover control (6-3A) defines the frequency at which audio below below the setting is routed to the LFE channel and audio above is sent to the Lf, Rf, C, Ls, and Rs channels. The crossover is typically set between 60 and 100Hz. This control works in combination with the LFE Routing and LFE Gain controls to create the LFE Channel.

Mid-Bass Crossover

Audio sent to the Center channel is split into two bands, LF and HF. The Mid-Bass Crossover control (6-3B) defines the crossover frequency of the split.

Splitting the Center channel into two bands allows the user to freely control the width of each frequency band accross the Center, Left, and Right soundstage.

This can be very useful in keeping the main phase-correlated signal (HF band) in the Center Channel for dialog while spreading the lower frequency portion of the Center channel audio (the LF band) - which could still contain some low-frequency dialog along with music and effects - accross all three front channels.

LFE Routing

The LFE Routing control (6-3C) balances the amount of LFE content (audio below the LFE Crossover Frequency setting) sent to the LFE channel verses what remains in the Lf, Rf, C, Ls, and Rs channels.

Setting this control to 0.50 sends 50% of the audio below the LFE Crossover the LFE channel and leaves 50% in Lf, Rf, C, Ls, and Rs channels. A setting of 0 sends no audio below the crossover frequency to the LFE channel, while a setting of 1 sends all audio below the crossover frequency to LFE channels, effectively removing it entirely from the remaining channels.

LFE Gain

The overall gain level of the LFE channel is set by the LFE Gain control (6-3D) and is typically set at a value of 0dB.

Center Width Controls

These controls define the routing of the Center channel LF and HF bands across the Left, Center, and Right channels. Used in combination with the Mid-Bass Crossover frequency control, they provide the ability to craft the image of the Front channels in a way that maintains a direct sonic-visual association of dialog while providing a pleasant and wide image of the phase-correlated elements. Values are expressed in a decimal format but easily correlate to a percentage value (0.00 = 0%, 0.50 = 50%, 1.00 = 100%, etc.).

The LF Center Width control (6-4A) determines the amount of LF audio routed to the Center versus the Left and Right Channels.

The HF Center Width control (6-4B) does the same for audio in the HF band.

A setting of 0% sends all audio in the respective band to the Center channel, while a setting of 100% sends audio to the Left and Right channels only. Intermediate values provide a blend to create any desired mix.

Auto-Detect Controls

When the Input Format is set to Auto-Detect, the UPMAX ISC continuously monitors the input signal to determine its format and will automatically switch between upmixing to the selected Output Mode and pass-through.

The level at which the detector circuit determines that the incoming signal is program audio (and not noise or silence) is set by the Auto-Detect Threshold control (6-5A). The proper setting depends largely on the quietness (or noisiness) of channels that are not muted but also contain no audio. Set too low, it may cause a false trigger to upmix; set too high, it may cause a late transition to upmixing. The default value of -70dB should work well for modern production while values as high as -63dB may be required for noisy sources.

The amount of time in milliseconds a signal must stay above the Auto-Detect threshold before the unit begins upmixing - or below the threshold to cease upmixing - is determined the Input Switch Transition control (6-5B). A value between 10ms and 12ms is a good starting point for most material.

The Advanced parameters are included for audio experts who wish to dig deep and tweak settings for very specific applications or demanding tastes. They are not required for most users and are accordingly not displayed by default.

NOTE: Some advanced controls - specifically those relating to additional side and height channels - will be grayed out if they are not applicable to the selected output format.

Cycles per Octave

The Cycles per Octave control (6-6A) defines the number of teeth there are in one octave of frequency change of the comb filter. The comb filter is used to separate different frequency components of the input signal to aid in steering sounds in the surround field.

Minimum Comb Filter Frequency

The lowest frequency of the comb filter is set by the Minimum Comb Filter Frequency control (6-6B). For most applications, this should be set at or near the same frequency as the Mid-Bass Crossover frequency.

Comb Filter Level

The Comb Filter Level control (6-6C) sets the overall level of the comb filter. This control can have a significant impact on the movement of audio between the front and rear channels, with higher values rendering a greater sense of depth. In nearly all cases, leaving this control at its default value will result in the most pleasing soundfield.

Front-Rear Balance Factor

The Front-Rear Balance Factor control (6-6D) determines the amount of upmixed sound pushed to the surround channels (analogous to the Surround Depth control in previous UPMAX versions). A value of 0 sends all audio to the Rear channels while a value of 1 sends no audio to the Rear channels. A value of 67 sends 33% of the audio to the Rear channels and keeps 67% of the audio in the Front channels.

Center Channel Gain

The Center Channel Gain control (6-6E) sets the volume of the Center channel created by the upmixer, which is typically dialog.

Rear Channel Downmix Level

In order for a stereo downmix to render at the same level as the original stereo source that was upmixed, the gain applied to the rear channels must be the inverse of the Dolby Rear Channel Downmix Level.

The Dolby standard Ls/Rs downmix level is -3dB, and so the Rear Channel Downmix Level control (6-6F) should be set to +3dB. Changing this setting by a small amount (-3 to +3) from the recommended +3 setting will not have a significant effect on the downmix, but can have a great effect on the upmixed presentation.

Front-High Crossover

The Front-High Crossover control (6-6G) adjusts the crossover point between the Front Left and Right channels and the Front Height channels when upmixing to 5.1.2, 5.1.4, and 7.1.2 formats. The crossover is very gentle and the effect of this control is subtle. The audio spectrum in the Front Height channels is determined by a combination of this control and the Lows in Heights control (described below).

Side-Rear Filter Crossover

The Side-Rear Filter Crossover control (6-6H) adjusts the crossover point between the Left and Right Surround channels and the Left and Right Back channels when upmixing to 7.1, 7.1.2, and 5.1.4 output formats.

Side-to-Rear Gain LF

The Side-to-Rear Gain LF control (6-6I) adjusts the gain of the low-frequency content in the Surround and Rear channels when upmixing to 7.1 and 7.1.2 output formats.

Side-to-Rear Gain HF

The Side-to-Rear Gain HF control (6-6J) adjusts the gain of the high-frequency content in the Surround and Rear channels when upmixing to 7.1 and 7.1.2 output formats.

Rear Channel Boost

The gain of the Left Rear and Right Rear channels when upmixing is set by the Rear Channel Boost control (6-6K).

Highs in Laterals

The Highs in Laterals control (6-6L) determines to what degree higher frequencies from the ear-level to height speaker crossover circuit are mixed back into the ear-level speakers when upmixing to 5.1.4 and 7.1.2 output formats. The audio spectrum in these channels is determined by a combination of this control and the Lows in Heights control (described below).

Lows in Heights

The Lows in Heights control (5-6M) determines to what degree lower frequencies from the ear-level to height speaker crossover circuit are mixed back into the height speakers when upmixing to 5.1.4 and 7.1.2 output formats. The audio spectrum of the Front Height channels is determined by a combination of this control and the Highs in Laterals control (described above).

Ceiling Speaker Gain

The Ceiling Speaker Gain control (6-6N) determines the amount of gain added to the Height channels when upmixing to 5.1.4 and 7.1.2 output formats.