What is an Upmixer?
An upmixer delivers multichannel sound from two channels of stereo input. Upmixers help overcome many limitations of the automotive environment. Upmixers deliver symmetrical stereo presentations for multiple listening locations, and they increase the apparent size of the vehicle cabin.
This internal Upmixer is very flexible and can be configured to enable a variety of systems. The front left, right, and center channel outputs of the Upmixer deliver the stereo presentation. The rear surround channels increase the apparent size of the cabin by enhancing ambiance. The Upmixer is configured from within the Mixer.
What Upmixed System Configurations are supported?
⁃ Front Stereo, Center-channel, and Sub (3.1)
⁃ Front Stereo, Rear Surround, and Sub (4.1)
⁃ Front Stereo, Center-channel, Rear Stereo, and Sub (3.2.1)
⁃ Stereo, Center, Rear Surround, and Sub (5.1)
⁃ Stereo Front, Stereo Rear, Rear Surround, and Sub (6.1)
⁃ Stereo Front, Stereo Rear, Center, Rear Surround, and Sub (7.1)
The configurations below all include a subwoofer, but the Upmixer does not provide a dedicated “.1” subwoofer channel - that is still defined in the Mixer. The upmixer can also be used without a subwoofer if desired.
The Upmixer-processed channels can be routed to any desired output channels. Once processed, they can be divided into band-limited, driver-specific channels using crossover filters. The Front Stereo can be full-range, active 2-way, or active 3-way, for example. The Center can be full range or active 2-way. Even the Rear Surround could be configured in this way, although this would be rare in practical application.
With traditional stereo systems, an active tweeter arrangement can be very valuable. With upmixed systems, the greatest value is to have sufficient power for the center, and to use an active 2-way center arrangement whenever possible. Active front Left and Right arrangements are not as important as an active center arrangement. It is always better to bridge to the center for more power than to have an unused stereo channel.
NOTE: Some premium OEM systems license sophisticated upmixer algorithms. If the vehicle you are working with has an advanced upmixed OEM system, it is often simpler to retain it and pass it through to the upgraded high-fidelity system being installed, rather than to try to return that signal to stereo so the internal Upmixer can be used. Many OEM upmixed systems use processing which cannot be properly reassembled into full-range two-channel stereo.
IMPORTANT: OEM systems often have non-entertainment sounds added to various channels. Do not eliminate any infotainment or safety audio content! Often, OEM center channels contain telematics emergency-call audio, and rear speakers contain often rear parking sensor audio. Ensure that these systems operate properly!
This Upmixer can be used with either the Master analog Source, the Optical digital Source, or both.
NOTE: There is one Mixer configuration for the Master Input, which is active whenever the Master input is selected. There is another Mixer configuration for the Optical input, and it is active as long as the Optical source is selected (in both cases, this setting affects all Memory Presets). This means that an OEM upmixed system can be passed through as the Master Source, without using the internal Upmixer - but an Optical source can be routed through the internal Upmixer if desired.
If the user desired one Memory Preset with upmixing and another Memory Preset with a traditional one-seat tune, lower the Center output channels to -40dB for the non-upmixed preset.
NOTE: Rear ambiance channels can be effective regardless of whether or not a center speaker is used. 4.1 and 6.1 systems using rear surround channels for ambiance can provide great one-seat performance without a center speaker.
Configuring the Upmixer
The Upmixer provides best results with 2 channels of flat, full-range, time- and phase-aligned signal. When using OEM signals, channels should be summed together to full-range, and corrected back to a flat frequency response and aligned phase and time response.
NOTE: With some modern vehicles, this may require some manual correction of phase and time. Always confirm phase and time linearity before you begin tuning.
There is a center-width setting for the Upmixer under “Features”. The most precise imaging is achieved with the “Narrow” setting.
NOTE: The subwoofer channels can be derived either directly from any Input channel, or from the outputs of the Upmixer, as desired.
IMPORTANT: OEM infotainment systems often use specific audio channels of the OEM system for non-entertainment sounds. Examples include center speakers playing telematics emergency handsfree-call audio, and rear speakers playing collision-alert notifications. NEVER disable any OEM safety system - always retain all emergency audio and all safety notifications.
This may require you to retain the OEM upmixer rather than the internal Upmixer described here, or it may require you to derive your own rear surround channels (see “7.1” below).
► 3.1 Front Left / Front Center / Front Right / Sub
- Go to the Mixer and Route the Front Left and Front Right inputs into the Upmixer in the Mixer, as shown.
- Use the Front Left and Front Right outputs of the Upmixer to supply signal for the Front Left, Front Right, and Subwoofer channels.
- Use the Center output of the Upmixer to supply signal for the center channel(s).
► 3.2.1 Front Left / Front Center / Front Right / Left + Right Stereo Rear / Sub
- Route the Front Left and Front Right inputs into the Upmixer in the Mixer, as shown.
- Use the Front Left and Front Right outputs of the Upmixer to supply signal for the Front Left, Front Right, and Subwoofer channels. Use the Center output of the Upmixer to supply signal for the center channel(s).
- Use the Rear Left and Right inputs to supply signal directly to the Rear Left and Rear Right channels. Do not go through the Upmixer.
► 4.1 Front Left / Front Right / Left + Right Rear Ambiance / Sub
- Route the Front Left and Front Right inputs into the Upmixer in the Mixer, as shown.
- Use the Front Left and Front Right outputs of the Upmixer to supply signal for the Front Left, Front Right, and Subwoofer channels.
- Use the Left Surround and Right Surround outputs of the Upmixer to supply signal for the Rear Left and Rear Right speakers.
► 5.1 Front Left / Front Center / Front Right / Left + Right Rear Ambiance / Sub
- Route the Front Left and Front Right inputs into the Upmixer in the Mixer, as shown.
- Use the Front Left and Front Right outputs of the Upmixer to supply signal for the Front Left, Front Right, and Subwoofer channels.
- Use the Center output of the Upmixer to supply signal for the center channel(s).
- Use the Left Surround and Right Surround outputs of the Upmixer to supply signal for the Rear Left and Rear Right speakers.
► 6.1 Front Left / Front Right / Left + Right Stereo Rear / Left and Right Rear Ambiance / Sub
- Route the Front Left and Front Right inputs into the Upmixer in the Mixer, as shown.
- Use the Rear Left and Right inputs to supply signal directly to the Rear Left and Rear Right channels. Do not go through the Upmixer.
- Use the Front Left and Front Right outputs of the Upmixer to supply signal for the Front Left, Front Right, and Subwoofer channels.
- Use the Left Surround and Right Surround outputs of the Upmixer to supply signal for the Rear Left and Rear Right speakers.
► 7.1 Front Left / Front Center / Front Right / Left + Right Rear / Left and Right Rear Ambiance / Sub
- Route the Front Left and Front Right inputs into the Upmixer in the Mixer, as shown.
- Use the Front Left and Front Right outputs of the Upmixer to supply signal for the Front Left, Front Right, and Subwoofer channels.
- Use the Rear Left and Right inputs to supply signal directly to the Rear Left and Rear Right channels. Do not go through the Upmixer.
- Use the Center output of the Upmixer to supply signal for the center channel(s).
- Use the Left Surround and Right Surround outputs of the Upmixer to supply signal for the Rear Left Surround and Rear Right Surround speakers.
IMPORTANT: If the OEM rear channels contain essential non-entertainment sound - or if OEM fader functionality must be retained - there is another approach that can be used for rear surround speakers.
- Set each rear surround speaker to derive 66% of its signal from the corresponding rear input. For example, set the Left Rear Surround speaker to receive 66% of the Left Rear input.
- Then set the same channel to receive 34% of the opposite channel. For example, set the Left Rear Surround speaker to receive 34% of the Right Rear input channel.
- Then use the inversion switch as shown to invert that opposite-side signal. Set up the opposite-side rear surround speaker in the same way - 66% signal from the same side, 34% inverted from the opposite side.
- Then set the delay for these rear surround channels to some value between 8 and 12mS. Play them just loud enough to help widen and deepen the stage, but not so loud that the rear speakers sound unnatural.
How do I tune Upmixed Systems?
The process of tuning an upmixed system is very different than tuning a driver’s-seat 2-channel system - but it’s not necessarily as difficult to perform. With a driver’s seat 2-channel system, the center image is not in the center of the stage unless we match left and right frequency response, level, and arrival times for the intended listening position. With an upmixed system, the center is in the center laterally because we have a speaker there - in the center of the dash. Now all we have to worry about is center level (to achieve the proper stereo imaging and avoid the “black hole” effect, where the center pulls everything in), the frequency response of the various speakers, and the frequency response of the overall system.
The center speaker is the most critical sound-quality speaker in the system.
Great results can be achieved with upmixers without any use of delay. If delay is used, symmetrical left/right delay is recommended to address transition-band cancellations. Using traditional distance-based asymmetrical delay to address left/ right passband cancellations ruins the symmetrical nature of an upmixed system. (This is a good application for all-pass filters).
NOTE: When configuring an upmixed system, do not enter the distances to any listening position into bit Drive! Many tuners succeed with upmixed systems using no delay at all.
One effective approach is to tune each front channel for the near listener. Since upmixed systems can be thought of as recreating the experience of listening to a performance from the audience in a slightly off-center seat, the near front speakers and the center are more critical than the far front speakers.
Put the mic in the driver’s seat. Play mono pink noise. Mute all speakers but the driver’s side Front. Tune the driver’s side to the target, adjusting output level and EQ as needed.
When the driver’s side matches the target, copy the driver’s side EQ and level settings over to the passenger side. (This is practical since vehicles are generally symmetrical longitudinally. Don’t worry about the steering wheel.) Do not use channel linking, as it will make the use of all-pass filters more difficult later in the process.
(Tuning Upmixed systems continued)
Play both left and right front. Look for cancellations, especially for one in the 200-300 Hz region. To predict the frequency of these cancellations more precisely, measure the distances to the front left and front right speakers from a listening seat, and subtract to find the path-length difference. Use the Technical Document “Path Length Cancellation Chart” to find the cancellations caused by this path-length difference. Test 2nd-order all-pass filters on the worst cancellations and verify that the response is improved. (This method is often only used on the first cancellation, in the 200-300 Hz region, to improve the midbass).
Now play the center speaker. EQ the center to the same target. Many tuners may add a 6dB dip at 2500 Hz to the center-channel response.
Since many center speakers are smaller than the front stereo speakers, and cannot use the same highpass crossover point, there may be a phase cancellation at the crossover point in the stopband region of the center highpass crossover filter. Look for this with the center and the driver’s side speaker playing. A first-order all-pass filter can be used on the center output channel to invert polarity below a specific frequency and address this phase issue.
Remove the mic and listen in the driver’s seat. Adjust the level of the center and the sides to ensure that left center sounds are directly in front of the left seat, and right center sounds are directly in front of the right seat. If these sounds are too close to the center speaker, that means the center speaker is too loud relative to the fronts. If these sounds are too far from the center speaker, that means the center is not loud enough relative to the fronts.
Once this level is correct, also play the rear speakers. Adjust the level to ensure that these rear speakers are loud enough to add ambience, but not loud enough to damage the stereo presentation up front.
When listening for bass up front, use of a 2nd-order allpass filter on top of a front/sub cancellation to restore phase alignment can be very effective.