RM-CG Voice Lift System Ver. 1.
Table of Contents Introduction................................................................................................................. 3 Purpose of Voice Lift .............................................................................................. 3 Two Use Cases of Voice Lift System ...................................................................... 3 Importance of Microphone and Speaker Placement and Sound Adjustment ...............
Introduction The RM-CG ceiling microphone is equipped with a "multi-beam tracking" function that provides stable tracking to multiple participants talking at the same time. It also delivers clear sound by making full use of its various audio processing technologies. We have received inquiries about the possibility of realizing a voice lift system in a classroom or meeting room by optimizing these features of the RM-CG.
Yamaha recommends using the RM-CG for voice lift within a presentation system. The RMCG dynamically detects the direction of a person speaking and picks up and tracks the sound by centering four beams on that person with enhanced directivity.
Result of Sound Pressure Increment on Voice Lift System with RM-CG and Ceiling Speakers Sound pressure increment was measured in the following system.
When a system needs to increment the sound pressure as high as possible, and is adjusted so each speaker can obtain a similar amount of loop gain, the sound pressure level at each sound receiving point (4.5 meters away from the RM-CG) is incremented by 7dB - 8dB. The further the distance between ceiling speakers and a microphone, the less feedback the speakers produce, as less sound is diffracted. Therefore, greater sound pressure levels can be expected at the back of the room.
System diagram RM-CG and Speaker Positions PAG and NAG For a voice lift system, install an RM-CG on the ceiling close to a presenter, and install speakers so every participant can hear the presenter's voice. The most challenging thing when designing a voice lift system is to obtain sufficient sound pressure levels without causing feedback. Feedback is usually caused by several factors such as distance between a microphone and speakers, the distance between a microphone and presenter, etc.
Elements Required for PAG/NAG Calculation The following seven elements are needed for PAG/NAG calculation.
Addition of CMM to PAG Formula: CMM is not usually added to the PAG formula because an omnidirectional microphone is commonly used. Since the RM-CG with sharp directivity is less prone to produce feedback, a +10dB margin is added as CMM according to the microphone characteristics. CMM is a margin only for the RM-CG based on the microphone characteristics and an actual measurement value.
Installation Environment Room Size A small room may not achieve enough sound pressure increment as more sound will be diffracted due to the RM-CG and speakers that are placed closer to each other. Therefore, if you are designing a system for a room with less than 10m depth, please reconsider if a voice lift system is really needed as a presenter's voice can directly reach all the participants in the room and may not need to be amplified.
Tracking Area Settings Since a voice lift system amplifies sounds picked up by the RM-CG, the RM-CG must be set so the sound will not be picked up again. The RM-CG has a function to narrow down the pickup area by specifying the tracking area of the microphone. For a presentation system, set the tracking area only to the point where the presenter is standing.
The following are the four important elements when designing and adjusting a voice lift system. 1. Room EQ settings to flatten the frequency response in the room Use an acoustic adjustment tool such as a real-time analyzer as well as a room EQ to flatten the system's frequency response as much as possible according to a room's acoustic character. The flatter the frequency response is, the more feedback margin can be achieved. 2.
Supplementary Audio Installation of Sub-speakers in Front A voice lift system with the RM-CG and ceiling speakers may not deliver sound at a sufficient volume level to the listeners in front. Ceiling speakers or VXL1-16-Ps installed in front for supplementation (see the figure above) can resolve an unusual situation where the listeners in front hear the presenter’s voice from behind.
To Stream Presentation to Remote Participants A voice lift system that can deliver presentations to remote locations requires more advanced design and adjustment techniques but with some limitations. The following are the elements that need to be considered. • Use the RM-CG's internal AEC that is optimized for the RM-CG. • Since RM-CG's Dante CH1 outputs audio with AEC processed, route audio from Dante Output CH1 to remote locations. • Return only the reference signal of the far-end signal to AEC.
Ducker can reduce audio deterioration mentioned above as it stops amplifying voice lift with • the trigger of audio signals from the far end. However, there is the following limitation. When a double-talk occurs (when both near-end and far-end speakers are speaking at the same time), for example when a near-end speaker starts speaking while a far-end speaker is speaking, the near-end speaker's voice will not be amplified by the voice lift system.
