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. The goal is to lift a presenter's voice just enough to maintain intelligibility for the furthest listeners, 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. 

The industry generally defines system gain as follows:

• Voice Lift: 6 to 12 dB of system gain. The goal is transparency; it should feel as if the presenter's unamplified voice is simply carrying further.
• Speech Reinforcement / PA: More than 12 dB of system gain. At this level, the amplification is no longer transparent and is clearly a public address system.

Q: What is required of the presenter in a PPL system?
A: The presenter needs to present clearly and at a reasonable volume. The system is designed to lift a normal speaking voice, not amplify a whisper. The target speaking level for a presenter should be approximately 60 dBA slow at 1 meter. If the presenter speaks too quietly, the system will have insufficient signal to lift effectively above the room's noise floor.

• This returns us to the Signal-to-Noise Ratio point from above, the PPL presenter needs to be 10-20 dB above the noise floor at the presentation stage area.
• If the noise floor is 40 dBA slow at the stage area and the presenter presents at 60+ dBA slow, there should be ample SNR for the PPL microphone(s).

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: How important is the commissioning process to a PPL system's success?
A: It is absolutely critical. Approximately 80% of a PPL system's success is dependent on the skills of the team deploying and commissioning it. This is not a "plug-and-play" or "check-the-box" feature. Success requires careful execution across all project phases, from initial site survey and noise floor measurement to precise installation and detailed audio tuning. Effective communication between the survey, installation, and commissioning teams is essential.

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 likely create an unstable feedback loop. Audience microphones should be configured for far-end conferencing only.

 

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 the TesiraFORTÉ X and Tesira VOLTERA D/DM (in special cases) platforms or systems that include these.

Q: Can I integrate PPL into an existing Dante-based system (e.g., a TesiraFORTÉ DAN)?
A: No, Parlé microphones require a bidirectional AVB connection for both audio and control data, including the critical back-channel information that freezes beams during far-end speech. TesiraFORTÉ DAN is not capable of supporting this AVB bidirectional communication. If Dante connectivity is a requirement for other parts of the system, a TesiraFORTÉ X can be used to handle all PPL and conferencing processing while also adding Dante network connectivity options.

Q: Can I use AI Noise Reduction in the PPL signal path?
A: No. The AI Noise Reduction algorithm introduces significant processing latency (approx. 53ms), which is typically unacceptable for local reinforcement. AI Noise Reduction should only be used in the signal path going to the far-end (e.g., USB or VoIP outputs).

• The standard Noise Reduction included within the AEC block has minimal latency and is used in the PPL signal path.
  • AEC Noise Reduction will likely be set to Low or Medium to help remove steady-state room noises. Setting this to High may help with other transient noises.

Q: What is the typical DSP resource usage for a PPL system?
A: DSP usage is significant and must be planned for carefully. The extensive per-channel processing for zoned loudspeakers consumes siginifcant core DSP resources. For example, a system with 12 individually processed loudspeaker zones can consume over 75% of a TesiraFORTÉ X 400. In many cases, a PPL system will require multiple TesiraFORTÉ X processors or a server-class device to accommodate both the PPL and any additional conferencing requirements. The new Presentation Space Designer tool does not calculate DSP usage; this must be verified by compiling the file in the Tesira software during the design phase of the project.

Q: Can I use a Tesira Launch report to survey a room for PPL?
A: Yes, a Launch Advanced report card can be a useful tool for gathering baseline acoustic data like Noise Floor and RT60 during the survey phase. However, it is critical to understand that PPL and Launch are not connected features. There is no "launch button" for PPL. The Launch report can help determine if a room meets the acoustic prerequisites, but the PPL system itself requires manual commissioning and tuning.

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 for a fixed lectern where it can provide superior performance compared to a standard gooseneck microphone. There are also cases where Parlé TTM-X may provide strategic coverage of instructional whiteboards. If a whiteboard camera is deployed, a TTM-X may be a good recommendation.

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. Field testing has shown that user preference for delay varies; some find it enhances the experience, while others do not perceive a significant benefit. It is an adjustment that can be made based on the specific room and listener feedback.

 

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: Physical orientation is required for beam aiming and consistency. The standard practice is to orient the microphone so the red alignment LED points toward "room north" (the main presentation screen or stage).

1. In the Parlé Mic block's control dialog, enable Orient Mics mode.
2. The microphone will illuminate a red LED segment and a green LED segment.
3. Physically rotate the microphone canister in its ceiling housing until the red LED points directly at the presentation screen ("room north"). The green LED will then point to the back of the room ("room south").
4. This ensures that the physical microphone orientation matches the default orientation in the software and design tools, creating a consistent reference for all technicians involved. It's very helpful when all team members involved in the project use the same reference point.

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 the PPL signal to these loudspeakers presents an unnecessary feedback risk. The Presentation Space Designer tool will calculate these attenuation values based on the room and device geometry you provide; make sure the device position measurements are accurate!

Tuning and Performance

Q: Must I lock the microphone beams for PPL? Can't I just let them track the talker?
A: Yes, PPL beams must be locked. When left in its default tracking state, a Parlé microphone behaves like a very smart omnidirectional microphone, which works against stability in a voice lift scenario. By locking the beams and aiming them specifically at the presentation area, you gain an immediate 1 to 3 dB of stability. Remember that beam locking and aiming can be recalled via presets in Tesira. This allows for different room usage and configuration modes.

Q: How does the Frequency Shift block work?
A: The Frequency Shift block prevents a feedback loop from building into an audible ring. It takes the incoming audio signal and shifts its frequency down (or up) by the defined amount. If that signal loops back through the microphone, it is no longer at the same frequency as the original source, so it cannot sum and build into runaway feedback. It is important to note this is a frequency shifter, which moves the entire audio band by a fixed amount, not a pitch shifter, which adjusts maintaining harmonic relationships.

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: Why do I need to "ring out the room" with notch filters if the Frequency Shift block prevents feedback?
A: The Frequency Shift block prevents feedback by shifting the frequency of the audio signal on each pass through the system, preventing a resonance from building at a single frequency. However, "ringing out the room" first provides two key benefits:

1. Additional Gain: Properly notching out the room's primary resonant frequencies with PEQ filters can add another 1 to 3 dB of gain before feedback.
2. Reduced Artifacts: An overdriven Frequency Shifter can produce audible artifacts which can be distracting to people in the room. By reducing the system's natural resonances, the system will be more stable and transparent to the audience and users.

Q: How do I "ring out the room"?
A: With the Frequency Shift block bypassed, slowly increase the PPL master gain until feedback begins. Using a measurement device (e.g. sound level meter or FFT program), identify the ringing frequencies and apply narrow parametric EQ (PEQ) filters to notch them out.

• Suggested starting point: -6dB to -10dB of cut with a Q (bandwidth) of approximately 0.15.
• Repeat the process until the top 4-7 resonant frequencies have been identified and notched. These are commonly found in the 200 Hz - 1200 Hz range.
• Once complete, you can re-engage the Frequency Shift block.

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" or a dive-bombing sound instead of a constant ring. What is that?
A: That is the Frequency Shifter operating at the upper 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 (e.g., 6Hz), preventing it from building into runaway feedback. If you hear this, it is a clear indication that you are operating past the upper stable limit of the system. There are two things that can be considered to minimize this:

• Lowering the upper limit of the user facing PPL Master gain control.
• Adjusting the Frequency Shift block to use a more aggressive amount (e.g., 8Hz or 12Hz).
• Test each of these or a combination of them before finalizing your decision.

Q: Why is the Gating Automixer in Parlay Presenter mode recommended over a Gain Sharing Automixer?

A: A Gating Automixer provides superior rejection of unwanted noise. The cardioid pickup pattern of a Parlé microphone beam is rather wide at lower frequencies and can capture noise from the audience. A Gain Sharing mixer would keep the microphone partially open, allowing this noise into the reinforcement system. The Gating Automixer in the new Presenter Mode mode offers several advantages:

• Higher Minimum Threshold: The threshold is raised from -30dB to approximately -12dB, preventing low-level noise from opening the gate.
• Steeper Advantage Gain: The Advantage Gain is set to 5dB, making it more difficult for a second microphone to open a gate when one is already active.
• Deeper Off Attenuation: This provides a significant benefit to system stability by minimizing the amplification of ambient room noise.

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: What is a recommended user control for a PPL system?
A: A commissioned PPL system typically has about 6 dB of usable range. We recommend providing the user with a simple control that defaults to a nominal "0" level, with the ability to adjust +3 dB (for a full room) and -3 dB (for a sparse room). A TEC-X 1000 wall panel is an ideal interface for this type of simple level control. If a 3rd party control system is available, TTP can be used to offer the same system control to the end user.

 

Advanced Topics / System Integration

Q: Can I retrofit PPL into an existing Tesira AVB system?
A: Yes, this is possible, but it requires careful survey and evaluation as if it were a new opportunity. A successful retrofit will likely require hardware additions and significant rewiring. The integrator must verify:

• Speaker Zoning: An existing single-zone 70V/100V speaker system must be rewired to support a multi-zone configuration, likely requiring the addition of amplifiers like the AMP-450P.
• DSP Resources: 
  • PPL processing requires the Frequency Shifter block (TesiraFORTÉ X).
  • PPL is DSP-intensive; the existing Tesira system may not have sufficient resources, often requiring the addition of one or more TesiraFORTÉ X processors.
• Microphone Placement: Existing Parlé microphones may need to be relocated to optimize their position relative to the stage and loudspeakers.

Q: How do I integrate a PPL system with far-end video conferencing? Can I use the same microphones?
A: Yes, the same presenter microphones can be used for both PPL and far-end conferencing, but the signal path must be configured correctly. The PPL example file demonstrates this topology:

• The signal from the Parlé Mic block is sent to an AEC block first.
• The post-AEC signal is then split. One path goes through the PPL processing chain (Frequency Shifter, EQs, etc.) to the local loudspeakers.
• The other path goes to the far-end, typically through additional processing like AI Noise Reduction before reaching a USB or VoIP output block.
• Crucially, the PPL loudspeaker chain must not be routed back into the AEC reference. The AEC reference should only contain audio from the far-end participants and other program audio sources.

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