TeamConnect Ceiling 2 TruVoicelift. Sennheiser‘s Interpretation of Voice Lift.
Sennheiser electronic GmbH & Co. KG
Am Labor 1, 30900 Wedemark, Germany, www.sennheiser.com AN 1300 v1.0 | 05/21 TruVoicelift
TeamConnect Ceiling 2
Content
Introduction ...... 3
Voice Lift in General ...... 4 Difference to Sound Reinforcement (SR) ...... 4 Technical Challenges ...... 5 Distribution of Sound ...... 5 Room Characteristics ...... 7 Risk of Feedback ...... 8 PAG/NAG Calculation ...... 9
TruVoicelift Mode in TeamConnect Ceiling2 ...... 10 Automatic Feedback Protection ...... 10 Unique Frequency-Shifting Technique ...... 10 Mute Threshold ...... 10 Mute Interval Time ...... 10 Noise Gate ...... 11 Noise Gate - Threshold ...... 11 Noise Gate - Hold Time ...... 11 Advanced Exclusion Zones ...... 12 Priority Zone ...... 14 Additional TeamConnect Ceiling 2 Benefits ...... 16
Checklist for Voice Lift Design ...... 17
Glossary ...... 18
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Introduction
TeamConnect Ceiling 2 is the leading microphone solution for video and webconferencing around the world . The easy installation and integration combined with the most flexible beamforming tech- nology and advanced zone control distinguish this most powerful microphone from other offerings on the market . The new TruVoicelift feature ensures the best natural speech experience with an outstanding speech intelligibility . Your voice can be heard throughout the room, right to the back row of a classroom, lecture hall or larger boardrooms and more .
This document describes what voice lift means in a typical audio-visual (AV) application and which of the challenges an installer might face during the installation . TeamConnect Ceiling 2 with TrueVoice- lift technology makes setup and configuration a lot easier . Overview of TeamConnect Ceiling 2 Features
Automatic Beamforming Technology The revolutionizing beamforming technology records all the audio signals in the meeting room . By means of digital signal processing, the position of the person speaking can be determined at any time, regardless of whether he or she is sitting, standing or moving around . The voice is captured evenly throughout the whole room .
TruVoicelift This feature allows the person speaking to move freely without worrying about the technology, pro- viding perfect intelligibility for all participants and decreasing possible feedback issues . It allows to significantly increase speech amplification on-site and gives the option to get significantly louder than other solutions on the market .
Advanced Exclusion Zones With up to five advanced Exclusion Zones, the customer has 100% flexibility and can precisely define the position of noise sources to be ignored by the beam tracking (vertically and horizontally) in a new, visually powerful 3D optic via Sennheiser Control Cockpit .
Priority Zone 100% control by setting a particular area of a room as Priority Zone for the microphone beam to focus on . This zone will be handled prioritized in case of incoming audio signals from different positions in the room at the same time .
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Voice Lift in General
The application of voice lift was introduced to evenly distribute the presenter´s natural speech volume despite a long travel distance to the listener . A study has shown that a voice lift is typically needed from a distance of 8 m (26 ft) from the person presenting . In special situations, where a person does not talk loudly, voice lift can be beneficial in even smaller rooms (For example, in speeches by an authoritarian person where the speech volume is predominantly in low pitches) . The goal is always to achieve speech intelligibility for all participants in a room .
Difference to Sound Reinforcement (SR)
Often, traditional AV conference rooms are equipped with Sound Reinforcement Systems (SR) or Public Address (PA) Systems . Although these systems focus on audio transmission, they may not be suitable for meeting or presentation applications .
PA / SR System Voice Lift System
With a conventional PA/SR system, all signals The key of a voice lift system is to keep the received in the room are reinforced to the point level of speech at a constant level despite where even the most distant presenter can be various distances in the room - even so that understood . the voices appear as clear, close and natural as possible without a hint of an artificial note To achieve a sufficient Gain-Before-Feedback and feedback . (GBF), the microphones must be worn very close to the body . The front of stage loudspeakers have Voice lift system amplifies the audio signals to be quite loud to reach the far-end of the room . individually while increasing the speech level This leads to different volume levels in the room . by 3 to 6 dB above the noise floor .
The conversation of a presenter in front of a large Microphones and loudspeakers are divided audience is usually only possible unidirectionally into different zones and can be level controlled and makes the direct interactivity between the by external DSP . participants very challenging .
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Technical Challenges
Despite decisive advantages over a PA/SR system, there are technical considerations to be made when designing a typical voice lift application (see „Checklist for Voice Lift Design“) . These special demands are described in detail below and show the complexity that an intelligent voice lift system must deal with in order to be best equipped for everyday challenges .
Distribution of Sound
The Inverse Square Law (ISL) states that every doubling from the sound source reduces the sound pressure level by 6 dB . This means that the sound energy decreases in intensity with each additional square from the source when distributed over a larger area . Based on ISL, most voice lift applications are designed for rooms of 10 x 10 m (33 x 33 ft) or larger . The distance from the presenter to the farthest listener should be at least 8 m (26 ft) or more . Depending on the room acoustics, ambient noise and the presenter‘s speaking volume, a voice lift may also be required in a smaller room .
Inverse Square Law
- 6 dB - 6 dB - 6 dB
70 dB 64 dB 58 dB 52 dB
0 m (0 ft) 1 m (3 ft) 2 m (7 ft) 3 m (10 ft) 4 m (13 ft)
Calculation example At a natural speech level of 70 dB, different values arrive depending on the position of the listener . Every doubling of the distance means a loss of 6 dB at the same time . While no additional gain is required at a distance of 1 m due to the good speech intelligibility, at a distance of 8 m (26 ft) the direct sound will have a level of approximatly 46 dB with a delay of 23 ms . This leads to the fact that the loss of sound energy must be compensated by additional voice lift .
3 m (10 ft)
+ 0 dB + 6 dB + 9 dB
2 m (7 ft) 4 m (13 ft) 6 m (20 ft)
Distance to talker 0 m (0 ft) 1 m (3 ft) 2 m (7 ft) 4 m (13 ft) 6 m (20 ft) 8 m (26 ft) 10 m (33ft) Attenuation of level 70 dB 64 dB 58 dB 52 dB 49 dB 46 dB 43 dB Gain to be added 0 0 0 + 6 dB + 9 dB + 12 dB + 15 dB Approx . delay to be added 0 2 9. ms 5 .8 ms 11 7. ms 17 .5 ms 23 ms 30 ms
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Distribution of Sound with TeamConnect Ceiling 2
Zone Control The even distribution of sound in the room without feedback can be created by splitting the loudspe- akers and microphones into different zones . Considering the size and acoustics of the room, the number of listeners, the distance between microphones and loudspeakers, and the polar pat- tern of the chosen loudspeaker will determine the positioning and number of zones needed . In order to determine how loud your system needs to be for even coverage and speech intelligibility in the room, the Potential Acouastic Gain (PAG) and the Needed Acoustic Gain (NAG) need to be calculated first (see „PAG/NAG Calculation“) . Sound Control of the Presenter
Example: If the presenter is at the front of the room, the loudspeaker level can be distributed evenly increasing from this zone to the furthest listener . Depending on the distances of the speaker and the listeners, an ideal mix-minus is calculated in the DSP (Digital Signal Processing) and a well- balanced mix is distributed via a matrix mixer for each zone .
Mix-minus is muting or lowering the volume in speaker zones that have active microphones, eliminating the potential of feedback . Mix-minus is also used when incorporating more then one TeamConnect Ceiling 2 microphone zone for audi- Sound Control of the Audience ence participation .
Sound Control When operating multiple open microphones at the same time, the distribution of systems must always be balanced . As lively as the interaction between the speakers and the audience can be, it is important to manage the interaction between mcirophones and presenter . To manage active microphones and loudspeakers, it is recommen- ded to use external DSP for zone controlling with automatic mixers . This both improves intelligi- bility and scales GBF significantly . To give each loudspeaker zone the desired sub-mix, automixers are complemented with powerful matrix mixers . Using equalisers (EQ) and notch filters, mixed signals can be granularly fine-tuned to the given room size . Pick-up of Audience´s Voice
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Room Characteristics
While outside reflections are negligible due to di- stances, they are mandatory in an enclosed space when it comes to designing a voice lift system .
Nearly all surfaces contain properties that fun- damentally change the resonances at different frequencies . Depending on the surface, different phenomena can occur, such as reverberation, echo, standing waves etc . Controlling the phen- omena and making them acoustically consistent with the entire system can be a challenge . Intelligent Beamform Technology uses the To achieve the highest possible speech intelligibi- Reflection of Soundwaves lity, the background noise level of the room should not exceed 45 dBA . Based on ISL the distance from the presenter to the farthest listening person should be at least 8 m (26 ft) or more . Depending on the room acoustics, ambient noise and the presenter‘s speaking volume, a voice lift may also be required in a smaller room .
Adaptation to the Room Characteristics with TeamConnect Ceiling 2 The intelligent TeamConnect Ceiling 2 technology makes use of the reflective properties of a room . Even in rooms with many reflective surfaces, excellent speech intelligibility is achieved due to the narrow beam of 30° . This then allows the focused beam to pick up each individual‘s speech cleanly even when the presenter is standing with the back to the microphone (e . g . speaking and using a whiteboard at the same time) . Positioning of TeamConnect Ceiling 2 Depending on the room and ambient noise, as well as the orientation of the TeamConnect Ceiling 2, the „PAG/NAG Calculation“ decides on the posi- tioning of the loudspeakers to achieve the highest possible GBF . This way, every listener in the room hears the speaker‘s natural speech without inter- fernces .
Rule of thumb We recommend to install TeamConnect Ceiling 2 at a height of 3 m (10 ft) to achieve a coverage radius of 5 m (16 ft) and a coverage area of approx . 50 to 60 m² . (approx . 540 - 650 sqft) . Depending on the situation, those values can also be exceeded . You can see from a drawing how the required speech area corresponds to the range of the microphones . TeamConnect Ceiling 2 Coverage Area
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Risk of Feedback
Based on ISL, it is necessary to gain the level of the incoming sound to achieve good speech intelligi- bility . However, the reinforcement of sound is directly related to the feedback from the loudspeakers .
How does feedback occur? While exceeding the critical level the reproduced sound from the loudspeaker re-enters the microphone system, forming a continuous loop . Each doubling of the number of open microphones means that the system gain must be reduced by 3 dB to avoid the feedback .
Factors that might lead to feedback • Relative positions of microphones and sound reinforcement loudspeaker • Number of open microphones (NOM) • Polar pattern of microphones and sound rein- forcement loudspeaker • Acoustic conditions of the environment (rever- berance)
Automatic Feedback Protection with TeamConnect Ceiling 2 During pauses in speech the „Noise Gate Settings“ attenuate the reinforcement of background noise . This is especially important when several microphones are used simultaneously (see „Noise Gate Settings“) .
With TruVoicelift, a „Unique Frequency-Shifting Technique“ is used to reduce the risk of feedback while simultaneously increasing the possible GBF . In case of a accured feedback the „Mute Th- reshold“ feature temporarily shuts down the output of the microphone (see „Unique Frequency-Shif- ting Technique“) .
Nose Gate Settings TruVoicelift Settings
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PAG/NAG Calculation
Here you can see one PAG/NAG calculation example of a typical use cases with TeamConnect Ceiling 2 .
A PAG/NAG calculation is needed to determine if the system can provide sufficient voice lift to achieve good intelligibility . The goal is to achieve a value of >=0 dB after the PAG-NAG difference . This indicates a potentially stable Voice Lift system . If the value calculated is negative, the system is indicated as potentially unstable and could suffer from feedback and insufficient intelligibility .
The following formulas are needed to determine the PAG/NAG value:
PAG = 20*Log((D0 * D1)/(D2 * DS)) - 10*Log(NOM) - FSM NAG = 20*Log(D0 / EAD) PAG-NAG = x dB If x >= 0, this value indicates a potentially stable system . If x <0, this value indicates for a potentially unstable system, which leads to suffer from feedback . PAG/NAG Calculation Example for a Large Boardroom
D1 D1
TCC2 TCC2
Ds D2
EAD
D0 Distance (d) d in m (ft) D0 Talker <-> Farthest Listener 10 m (33 ft) D1 TeamConnect Ceiling 2 <-> Loudspeaker 3 m (10 ft)
D2 Farthest Listener <-> Loudspeaker 1 .8 m (6 ft) EAD Talker <-> Nearest Listener 3 7. m (12 ft) Ds Talker <-> TeamConnect Ceiling 2 2 m (7 ft) NOM Number of open Microphones 2
FSMTCC2 TeamConnect Ceiling 2 Feedback Stability Margin 6 dB Calculation Example PAG 20*Log((33 * 10)/(6 * 7)) 17 9. - NOM 10*Log(2) - 3 - FSM 6 - 6 - NAG 20*Log(33ft / 12ft) - 8 78. 0 .12
This example considers two open microphones (NOM) . Applying the formula, we obtain a value of 17 9. for PAG and 8 78. for NAG . If we subtract the NOM and FSM from PAG, we get a value of 8 9. . This value is larger than the achieved value of NAG (8 78). and means that there is enough voice lift to achieve good intelligibility without feedback . The acoustics of the room are always decisive for whether the positive value is sufficient for the calculated performance or not . You can find more information about PAG/NAG here .
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TruVoicelift Mode in TeamConnect Ceiling2
TruVoicelift offers the best solution for both conferencing and now in-room audio for classrooms, lec- ture halls, boardrooms and more . It allows the customer to significantly increase speech amplification on-site in the meeting room . In conjunction with flexible control, Exclusion Zones and a Priority Zone can be easily defined, and highly effective algorithms can be activated to control feedback . These and other features clearly set TeamConnect Ceiling 2 apart from the competition and contribute to a sound experience that has never been achieved by a ceiling microphone before .
Automatic Feedback Protection
When switching on TruVoicelift, different features are activated to automatically suppress the feedback . On the one hand, there is a special frequency-shifting procedure that is used automatically . The other is „MuteThreshhold“ and „Mute Interval Time“ adjust- ment .
Unique Frequency-Shifting Technique
TruVoicelift uses a unique frequency-shifting technique to activa- TruVoicelift Settings te certain algorithms to the microphone output signal in order to mitigate the risk of feedback from the loudspeakers in the room .
The occurring frequencies are shifted differently in real time while maintaining the voice quality . By shifting the frequencies, the risk of feedback is considerably reduced, as the wave transmission does not occur in one wave bundle, but in several wave portions . At the same time, it has the effect of achieving a higher gain .
The frequency-shiftig technique is used to achieve the best speech results . That means, that this method is ideally suited for voice lift application in meeting rooms of all kinds . It is not suitable for use in the context of professional music applications .
Mute Threshold
TruVoicelift has an inbuilt automatic mute function which will temporarily shut down the output in case the microphone level exceeds the set level of the Mute Threshold . This can be caused by an unexpected increase in volume . With the slider you can adjust the Mute Threshold according to the microphone level from -50 dB to +3 dB in steps of 3 dB .
Mute Interval Time
The Mute Interval Time allows to set a period of time for how long the microphone should be muted after the Mute Threshold has been exceeded . With the useful setting, a time can be set to restore the situation acoustically . With the slider you can adjust the interval time from 1 s to 30 s in steps of 1 s .
Recomendation: We recommend carrying out a test on site . Depending on the room acoustics, the test will turn out differently . Leave the value at -50 dB . To adjust the unit, clap your hand several times while gradually increasing the intensity of the impact . Observe at which value the system mutes the sound . With the „hand clap test“ a good noise level can be obtained to take as a starting value and to estimate a suitable Interval Time .
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Noise Gate
The Noise Gate ensures that the reinforcement of background noise is switched off during pauses in speech . This is especially important when several microphones are used simultaneously . During pauses in speech, the system usually reinforces the gain assuming that there is not enough sound pressure behind . Consequently, the background noise is reinforced unnecessarily .
Noise Gate - Threshold
To avoid this, a threshold can be set at which level the system should Noise Gate Settings mute the microphone . Furthermore, a Hold Time can be set, which will be necessarily observed . The Noise Gate will open the audio of the microphone output only after the predefined threshold value of the needed microphone has been exceeded .
With the slider you can adjust the minimum threshold level from -90 dB to -40 dB in steps of 1 dB .
Recommendation: To achieve the highest possible speech intelligibility, the background noise level of the room should not exceed 45 dBA . This is a good initial value to test and possibly adjust the noise level in the running meeting .
Noise Gate - Hold Time
This setting determines how quickly the microphone should be opened again . A delay of up to 1000 ms can be set . The Hold Time is adjustable between 50 and 1000 ms .
Recommendation: Depending on the type of speech and the surrounding noise, the opening of the microphone channel can be delayed . Our recommendation is to initially leave the setting at 50 ms to achieve the lowest possible latency . Depending on the situation and the type of speech, the value can be gradually increased .
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Advanced Exclusion Zones
The acoustic situation in meetings sometimes suffers from unwanted background noise, such as from the air-conditioning systems, side doors, loud coffee machines and adjacent rooms . Loudspeakers with far-end participant audio can also be a source of interference for the microphone . To suppress these unwanted background noises, you can define Exclusion Zones in which the audio signals are ignored by the beam tracing . With the alignment of vertical and horizontal zones, noise sources can be suppressed easily .
Maximum Flexibility with 5 Exclusion Zones With TeamConnect Ceiling 2, up to 5 exclusion zo- nes can be flexibly configured in relative position to the ceiling microphone . The Exclusion Zones are flexibly aligned vertically and horizontally and can all be activated simultaneously .
As soon as the unit is initialised, TeamConnect Ceiling 2 uses the real-time algorithm to detect the sources of interference, which are directly displayed in the Control Cockpit in a visualised
3D model . An Exclusion Zone can then be defined Automatic beam technology precisely and without much effort .
Flexible Coverage Area The vertical angle covers a range of 0° - 90° . The horizontal angle can be variably adjusted from 0° - 360° . With these coverage ranges, a complete hemisphere can be captured starting from the cei- ling microphone . The settings of individual zones are made in the Control Cockpit software with just a few mouse clicks .
Depending on the situation, the Exclusion Zones can be used for different voice lift scenarios: Adjustment of the vertical zone • If there is no noise in the room, the zones can remain switched off . • If permanently installed devices (e g. . air con- ditioners, loudspeakers) are to be excluded, it helps to set up a vertical zone as well as a horizontal zone in the corresponding height and width . • If several noise sources are present, several Exclusion Zones can be set up and used simul- taneously .
Adjustment of the horizonatal zone
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Example 1 - Small Classroom There is no potential noise in a small classroom . In this case, you can adjust an Exclusion Zone off of the ceiling to ignore the ceiling mount voice lift loadspeakers . To prioritise the teacher‘s voice, a „Priority Zone“ can always be set up, regardless of the Exclusion Zones .
Example 2 - Meeting Room The far-end audio of the loudspeakers in use result in a constant background noise that poses the risk of creating feedback . After setting up a vertical and horizontal Exclusion Zone for this area, no audio signals from this area are tracked by the beam any more .
Example 3 - Lecture Hall During a lecture, the permanent noise of the projector fan affects the constant activation of the microphone . By setting up an Exclusion Zone for the projector, the noise of the fan will be attenuated .
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Priority Zone
In lively discussions in a meeting, it is indispensable to have a moderator who continuously controls what is going on in the conversation . In order to not necessarily give immediate priority to a very strong voice based on volume, a Priority Zone can be set up . This allows the moderator to always give priority in perceiving incoming sounds, possibly despite a quieter voice . This ensures that the person in charge is always in control of the situation vocally .
Highlighting a Prefered Area The priority zone is used to keep the moderator‘s voice in focus constantly . For this purpose, the preferred zone is easily set up in the Control Cockpit, taking into account the activity radius of the moderator .
The dimension of the zone can be flexibly adjusted vertically up to 90° and horizontally up to 360° .
Furthermore, the weighting of the prioritised zone can be set . The weighting determines how intensi- vely the directed beam is to focus on this area . The following values can be set:
• Mid: Increases the weighting on the audio output from the zone by about 1 .5 times the normal value (e . g . in rooms with normal am- bient noise) . • High: Increases the weighting on the audio out- put from the zone by about 2 times the normal value (e . g . in rooms with loud ambient noise) • Max: Increases the weighting on the audio output from the zone by about 3 times the normal value (e . g . for rooms with high ambient noise and a lower volume presenter) .
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Example 1 - Classroom When integrating the system in a classroom, several TeamConnect Ceiling 2 units are used simul- taneously and divided into coverage zones . The first coverage zone includes the teacher‘s area . A Priority Zone is set up generously for this area, according to the teacher‘s typical movement in the room . Due to the disciplined behaviour towards a teacher in a classroom, the weighting can be set to „Mid“ .
Example 2 - Lecture Hall In a lecture hall, the number of persons is usually more than in a classroom . As a result, the potential noise level is most likely higher . The setting here can be set between „Mid“ and „High“ .
Example 2 - Boardroom In the case of lively discussions during a meeting, the controlled course of the conversation is usually omitted . For this purpose, it is suitable to set up a priority zone for a moderator and to set the setting to „Max“ . TeamConnect Ceiling 2 captures the full range of all participants, but gives priority to the established Priority Zone . This ensures that the situation is kept acoustically under control .
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Additional TeamConnect Ceiling 2 Benefits
Using traditional microphones the implementation of a voice lift system is a real challenge for instal- lers and sound engineers . Depending on the system design and environmental conditions, additional barriers arise with regard to feedback, ambient noise, maintenance, operation, hygiene etc . The following benefits arise by using TeamConnect Ceiling 2: + + Easy Handling Easy Setup and Maintenance Users do not have to be constantly The central positioning of the micropho- reminded of the correct handling, opera- ne on the ceiling makes the distribution tion, positioning or special situations (e . of individual microphones on the table g . feedback) . unnecessary .
Implementation into an existing network + does not require a complex installation Freedom of Movement with many criteria to consider as a sys- A ceiling microphone offers a high de- tem engineer . gree of flexibility for all participants . By With TeamConnect Ceiling 2 the entire means of digital signal processing, the maintenance effort as well as the addi- position of the person speaking can be tional personnel resources are omitted . determined at any time, regardless of whether he or she is sitting, standing or moving around . + No Concerns about Hygiene + Touchless audio systems are designed Automatic Adaptation to the Room for communication with several people No microphones need to be physically involved . The constant change of users adjusted if there is a reorganisation in requires continuous compliance with hy- the room . The system is configured via giene measures on the equipment used . Control Cockpit with just a few clicks .
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Checklist for Voice Lift Design
When considering a voice lift system, many criteria need to be taken into account . This checklist provides an overview of the most important points to consider when integrating the system .
All presenters and listeners in the room are taken into consideration. How many people will be speaking in the room and where is their audience? This question helps to determine the minimum space requirements needed and the requi- red coverage area of all people speaking . The number of microphones needed is determined. Is a microphone needed for the audience to interact with the presenter? This question helps to determine the amount of microphones needed to ensure proper interaction between the presenter and the audience . Planning for the microphone coverage is done. Has the distance between the microphones and the distance to the locally installed sound reinforcement speakers, presenters and audience been considered? The adequate positioning of the devices helps to ensure sufficient distance to pick up in- coming signals and to prevent potential feedback risks in advance . The speaker coverage and speaker zones are determined acc. to the listening area. From which directions do the speech signals come? This aspect helps to enable the best possible achievement of natural sound pressure . Based on the achieved value, the loss of pressure can be calculated according to Inverse Square Law . This value will be essential for the needed PAG/NAG calculation . The environmental conditions of the room are considered. Has the reverberation time (RT60) and ambient noise level of the room been determined? Reverberation is the collection of many sound reflections in a room . The „Reverberation time“ (RT60) indicates the period of time it takes for reflected sound to „ fade out“ in an enclosed space after the sound source has come to a standstill . The time results are significant in determining how a room responds to acoustical sound . Recommended RT60 values: Location Volume Critical Distance Dc Recommended RT60 Classroom < 200 m3 2 m 0 .4 - 0 6. s Office < 1'000 m3 3 .5 m 0 .5 - 1 1. s Lecture Hall < 5'000 m3 6 m 1 0. - 1 .5 s
All interacting systems have been identified. Will voicelift work with an existing conference system or DSP with AEC reference? Will remote participants be actively speaking? This question helps to identify all systems that are considered as potential audio signal inputs (including far-end signals) . These systems must then provide a balanced and har- monized distribution of sound in an overall structure . The Potential Acoustic Gain (PAG) and Needed Acoustic Gain (NAG) were calculated. What PAG/NAG level can be achieved based on the proposed microphone, speaker, and people placement? A PAG/NAG calculation is needed to determine if the system can provide sufficient voice lift to achieve good intelligibility . A value of >=0 dB after the PAG-NAG difference indica- tes a potentially stable Voice Lift system (see „PAG/NAG Calculation“) All clients expectations are managed. Were all the requirements met? Based on all the data collected (number of presenters/audience and their distances in the room, room characteristics, possible sources of interference, possible GBF, DSP mixing requirements etc .), the overall infrastructure created should be closely harmonized with the customer‘s expectations .
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Glossary
AEC Acoustic Echo Cancellation AEC is used to remove echoes, reverberation and unwanted additional noise from a sig- nal passing through an acoustic space . This function is mostly needed when a person is connected via a remote connection, known as Far End . EAD Equivalent Acoustic Distance Distance between the talker and un-aided listener . AV Audio-Visual Involving the use of recorded pictures and sound, or the equipment that produces them . dB Decibels A unit for measuring the loudness of sound . DSP Digital Signal Processing Used for digital encoding of “live” signals such as audio, video etc . and allows these signals to be stored, manipulated, edited, replayed, and transferred much more efficiently and accurately than by using strictly analog methods . EQ Equalizer Electronic equipment that adjusts (= makes slight changes to) the frequency of recorded sound to make it sound better . FSM Feedback Stability Margin Stability value which is determined and used for robustness against disturbances . GBF Gain-Before-Feedback A practical measure of how much a microphone can be amplified in a sound reinforcement system / voice lift system before causing audio feedback . NAG Needed Acoustic Gain Value in decibels which the system will require to achieve in order to perform effectively . PAG Potential Acoustic Gain Potential maximum amplification in decibels the system can apply before feedback occurs . PA Public Address System Equipment for making sound louder in a public place . SR Sound Reinforcement System System of microphones, signal processors, amplifiers and loudspeakers that ensures con- trolled mixing and distribution of live sound to a larger or more distant audience . RT Reverberation Time Is a measure of time required for reflecting sound to „fade away“ in an enclosed area after the source of the sound has stopped . RT60 Reverberation Time 60 Is the period of time required for the sound pressure level to decrease by 60 dB after a sound source is abruptly turned off . RT60 is common abbreviation for Reverberation Time .
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