Parlé Presenter Lift: Frequently Asked Questions (FAQ)

General Concepts / Is PPL Right for My Project?

Q: What is the fundamental difference between Parlé Presenter Lift and a traditional PA or Speech Reinforcement system?

A: PPL is designed for subtle, transparent reinforcement, not high-volume amplification. The goal is to lift a presenter's voice just enough to maintain intelligibility for the furthest listeners, typically aiming for a Signal-to-Noise Ratio (SNR) of 10 dB above the room's noise floor. It should feel natural, as if the presenter's voice is simply carrying further. A traditional PA system provides much higher gain and is not intended to be transparent.

Q: In what scenarios should I NOT use PPL?
A: You should not specify a PPL system if the room fails to meet the "Pillars of Success":

1. Poor Acoustics: If the room's noise floor is above 43 dBA or the RT60 is over 500ms, the system will likely not have enough stability to provide meaningful lift.
2. Small Room: If the distance to the furthest listener is less than 35 feet (10.7m), PPL will likely not have enough stability to provide demonstrable lift.
3. Unzoned Speakers: If the loudspeaker system cannot be discretely zoned and controlled, you cannot implement the gain mapping required for stability.

Q: Can a PPL system be used for audience microphones to reinforce audience questions?
A: No. PPL is a one-to-many system designed to lift a single source (the presenter) and distribute it to many listening locations (the audience). Attempting to use it as a many-to-many system by reinforcing audience members through the same loudspeakers would create an immediate and unstable feedback loop. 

 

Design and Hardware

Q: Can I implement PPL on a TesiraSERVER-IO or a legacy rack mounted TesiraFORTÉ (non-X)?
A: No. The Frequency Shift Feedback Suppressor block is essential for system stability and is only available on processors with newer DSP. This currently limits PPL deployments to the TesiraFORTÉ X and Tesira VOLTERA D/DM (in special cases) platforms or systems that include these.

Q: Does the Presentation Space Designer automatically calculate speaker delay for time alignment?
A: No, it does not. The designer focuses on microphone placement, beam aiming, and gain mapping. While adding delay to align the reinforced signal with the presenter's acoustic arrival time can improve localization in very long rooms, it is an advanced, optional tuning step that must be calculated and implemented manually. In many spaces, the audible benefit may not be significant enough to warrant the additional complexity.

Q: When should I choose a TCM-X/TCM-XA versus a TTM-X for PPL?
A: The Parlé TCM-X (ceiling microphone) is the primary choice for most PPL applications, as it provides excellent coverage for a presenter who moves around a stage or presentation area. The Parlé TTM-X (tabletop microphone) should be considered a special case solution, such as when placing it on a fixed lectern to provide lift for a presenter. In this lectern application, the Parlé TTM-X may perform better than a standard gooseneck microphone. 

 

Installation and Placement

Q: Why is placing the microphone at the "lip of the stage" so important?
A: This forward placement provides the best geometry for the microphone's beams to cover the entire presentation area, from the very front to the back. Crucially, it also helps to physically distance the microphone from the first row of loudspeakers, which are typically set to the lowest volume and pose the greatest initial feedback risk.

Q: I've installed the TCM-X, but the physical Biamp logo isn't facing the front wall. Do I need to re-install it?
A: Not necessarily, but very highly recommended. In the Parlé Mic block, use the Orient Mics LED mode to physically display the orientation of the microphones. At this point, the installation team can rotate the microphone's pickup pattern until the red LED aligns with the room's true/plan "north" (the presentation screen). Once this orientation is physically corrected, it will systematically align with the default color zoning in the Parlé Mic block. It's very helpful when all team members involved in the project use the same reference point.

 

Tuning and Performance

Q: Why do I need to "ring out the room" with the Frequency Shift block bypassed first?
A: The system won't "ring" with the Frequency Shifter engaged.  When the Frequency Shifter shifts the audio signal, it effectively moves any sinusoidal resonances in the system, thereby preventing a positive feedback loops or "ringing".

Q: If the Frequency Shift block prevents the system from "ringing", why do I need to "ring out the room" with notch filters?
A: Ringing out the room will potentially add 1-3 dB additional gain before feedback and will significantly reduce the workload on the Frequency Shifter.  While the Frequency Shifter works well, it can be audible and distracting to people in the room.  The combination of "ringing out the room" and the Frequency Shifter maximizes gain before feedback and keeps the signal as clean as possible.

Q: How do I "ring out the room"?
A: With the Frequency Shift block bypassed, push the PPL master gain level to the point when feedback begins to occur. Using a measurement device (e.g. sound level meter or FFT program), the ring frequencies can be identified and notched out using PEQ filters in the signal chain. The suggested depth is 6-10 dB with a bandwidth of 0.15.

Repeat the process until the top 4-7 ring frequencies have been identified and notched. In our testing, we've observed these will commonly be in the 200 - 1200 Hz range. Once notched out, the Frequency Shift block and AEC processing can be re-engaged and the system should have gained 1-3 dB of additional stability.

Q: The default Shift Amount is 6Hz. Can I use a higher value?
A: Yes, but with a trade-off. Increasing the shift amount (e.g., to 8Hz or 12Hz) can provide more stability against feedback. However, higher values can become subtly perceptible to listeners, creating a "chorusing" effect or slight tonal change that may cause listener fatigue over time. The 6Hz setting is the recommended sweet spot and default.

Q: When pushing the system gain, I hear strange "ghost trails" instead of a constant ring. What is that?
A: That is the Frequency Shifter doing its job at the absolute limit of stability. The "ghost trail" is the sound of an impulse looping through the system. Each time it loops, its frequency is shifted again by the defined amount in the Frequency Shift block, preventing it from building into runaway feedback at a single frequency. If you hear this, it is a clear indication that you are operating past the upper stable limit of the system.

Q: Why is Gating Automixer recommended over a Gain Sharing Automixer for PPL?
A: A Gating Automixer provides superior rejection of unwanted noise. During testing, it was found that the cardiod pickup pattern of a Parlé microphone could capture noise from the audience. A Gain Sharing mixer would keep the microphone partially open, allowing this noise into the reinforcement system. The adjustable threshold of a Gating Automixer (especially in the dedicated Parlé Presenter Mode) and deeper off attenuation provides a significant benefit to system stability and minimes audience noise from being amplified.

Q: What is the difference between "Gain Shading" and "Gain Mapping"?
A: The terms are often used interchangeably to describe the same technique. "Gain Shading" is a common industry term for progressively adjusting gain across multiple loudspeakers (like its use in line arrays). "Gain Mapping" can be thought of as the documented result of that process—a "map" of the specific gain values for each speaker zone in a particular room layout.

Q: Should loudspeakers very close to the presenter be turned completely off?
A: Yes. In most cases, any loudspeaker within approximately 12-15 feet (3.5-4.5 meters) of the active presenter microphone should be turned off (or attenuated to -100dB) within the PPL signal path. Listeners in this area do not need reinforcement, and sending PPL signal to these loudspeakers presents an unnecessary feedback risk. The Presentation Space Designer tool will calculate these attenuation values based on the input it receives. Be sure to measure the installed location of each loudspeaker and microphone and update the Presentation Space Designer accordingly for accurate calculations.

Q: Is there a recommended user control for a PPL system?
A: Yes, we've found that a commissioned and tuned PPL system often has about 6dB of usable gain. We refer to this as Nominal and Nominal+3/-3 dB. The TEC-X 1000 makes a perfect user interface allowing PPL level control within that usable range. It also offers opportunity for preset recalls as needed. 

 

Advanced Topics / System Integration

Q: How do I integrate a PPL system with far-end video conferencing? Can I use the same microphones?
A: While it is possible, it may be best to use dedicated microphones for the PPL system. If you must use the same microphones for both PPL and far-end conferencing, extreme care must be taken:

• You must create a separate signal path for the far-end.
• The audio from the PPL mics must be sent to the AEC block before it is sent to the local reinforcement speaker chain.
• The output of the PPL speaker chain must not be routed back into the AEC reference, as this would create a feedback loop for the far-end audio. This requires a complex Mix-Minus configuration within your Tesira file. (???? not sure about this one)

Q: Can I use Tesira Presets to change the locked beam configuration for a divisible or multi-purpose room?
A: Yes. The Enable Beam Aiming Lock state, as well as the individual Azimuth and Elevation settings for each beam, are all preset-controllable. This allows you to create different presets for various room configurations, such as re-aiming the beams from a "north" stage to a "west" stage when the room layout changes.

 

Further reading:

• Parlé Presenter Lift: Overview (Start Here)
• Parlé Presenter Lift: Site Survey and Preliminary Design
• Parlé Presenter Lift: Installation and Pre-Commissioning
• Parlé Presenter Lift: System Commissioning