Omni2 multichannel library
Contents
1. lt 7 UM1655 WI life augmented User manual Audio Engine post processing on STM32F4xx Omni2 multichannel library Introduction The Audio Engine post processing on STM32F4xx Omni2 multichannel library user manual describes the software interface and requirements of the Omni2 multichannel module It has been designed for the audio application developers who integrate this module into a main program It provides a rough understanding of the underlying algorithm The Omni2 multichannel library implements the multichannel audio virtualization from mono to 7 1 input signals including the stereo widening effect for stereo inputs This library is part of the STM32 AUDIO100A firmware package July 2015 DocID025072 Rev 4 1 26 www st com Contents UM1655 Contents 1 MOQUE OVEIVICW Camara wer wed a wee eee ee ee 6 1 1 Algorithm function ee eens 6 1 2 Module configuration aa aaaea 8 1 3 Resources summary eee 8 2 Module Interfaces cae co ech org peace atea oe ee a ec ee ae dede 10 2 1 APIS acres ear ae a a apa 10 2 1 1 omni2_reset function o o o ooooooooro eee 10 2 1 2 omni2 setParam function 0 0 0 0 10 2 1 3 omni2_getParam function 0 0 0 ee eee 11 2 1 4 omni2 setConfig function 0 0 ce ee 11 2 1 5 omni2 getConfig function o oooooooonrnene es 12 2 1 6 omni2 process function n sasaaa ae e eee 12 2 2 External definitions and types ccc eee 12 22. 2 1 Input and output buffers aaa 12 2 2 2 Returned error values eee 13 2 3 Static parameters structure 0 ea 13 2 4 Dynamic parameters structure a 14 3 Algorithm description 4 es 16 3 1 Processing steps eee eens 16 3 2 Data INE CPP PAA 16 3 3 Performance assessment cece eee 17 4 Application description 0 cee es 18 4 1 System requirements and hardware setup o o oooooooooo 18 4 1 1 Recommended setup for stereo widening effect 18 4 1 2 Recommended setup for multichannel virtualizer effect 19 4 2 Recommendations for an optimal setup o o ooo o 20 4 2 1 Memory allocation eee eens 21 4 2 2 Module API calls aaa kaa mam rca ana DADA WAWA ee KG 21 4 2 3 Module integration summary 0000 ee 23 2 26 DocID025072 Rev 4 Kyy UM1655 Contents 5 How to run and tune the application 24 6 REVISION NISLOTY ies see BRA bbb ee eee ee a 25 3 DocID025072 Rev 4 3 26 List of tables UM1655 List of tables Table 1 Sampling Tales APA abr dan ween oo ies 6 Table 2 Resources SUMIMANL o saccra sensia cw Sew ew eee yee Le Oe Re Be oom 10 O ee Da 8 Table 3 Frequency requirements MHZ 0 0 ccc a 9 Table 4 OMM VESEL Sir ABG a a ate hula nos a Aye wn Ws a A te A oe wes 10 Table 5 omn Seras mcivrar a nara rs boars Oe kee OE Eee Ea be eet 11 Table
3. provisions different from the information set forth herein shall void any warranty granted by ST for such product ST and the ST logo are trademarks of ST All other product or service names are the property of their respective owners Information in this document supersedes and replaces information previously supplied in any prior versions of this document 2015 STMicroelectronics All rights reserved 2 20 26 DoclD025072 Rev 4
4. 0 leads to the widest virtual angle typically 100 degrees Omni2ListeningAngle field from the module s dynamic parameters is modified by selecting between LargeSpacedS CloseSpacedS and VCloseSpacedS DoclD025072 Rev 4 Kyy UM1655 Revision history 6 Revision history Table 16 Document revision history e meros mes Updated Section 1 1 Section 1 3 Section 2 4 Section 4 1 1 Section 4 2 Section 4 2 2 Table 2 Table 3 Table 13 Figure 5 22 Jul 2015 4 Added Table 14 Removed section Recommended setup for stereo widening effect for closely spaced speakers Omni2DownFiringSpeakers set DoclD025072 Rev 4 25 26 3 IMPORTANT NOTICE PLEASE READ CAREFULLY STMicroelectronics NV and its subsidiaries ST reserve the right to make changes corrections enhancements modifications and improvements to ST products and or to this document at any time without notice Purchasers should obtain the latest relevant information on ST products before placing orders ST products are sold pursuant to ST s terms and conditions of sale in place at the time of order acknowledgement Purchasers are solely responsible for the choice selection and use of ST products and ST assumes no liability for application assistance or the design of Purchasers products No license express or implied to any intellectual property right is granted by ST herein Resale of ST products with
5. 0 degrees listening angles Figure 6 Setup for multichannel virtualizer effect Physical Speakers Physical Speakers Physical Speakers Largely Spaced Speakers Closely Spaced Speakers Very Closely Spaced Speakers MSv38405V1 DoclD025072 Rev 4 19 26 3 Application description UM1655 4 2 20 26 Table 15 Virtualized sound compliant with ITU T 7 1 speaker layout standards Physical Speakers 150 Deg Perceived Virtual Speakers N k N N MS32353V1 i e Front channels are at 30 Side channels are at 110 and Rear channels are at 150 Recommendations for an optimal setup The library processing should be placed just after the multichannel decoder and before the sampling rate conversion in order to process the audio signal at 32 44 1 or 48 kHz and avoid doing sampling rate conversions on multichannel Note that only 48kHz sampling frequency is supported in this SW version There is no need for this module to be close to the audio DAC and some graphical equalizer and volume management modules can be placed after it without affecting the widening or virtualization perception To integrate this module in an audio software framework follow the next steps 2 DoclD025072 Rev 4 UM1655 4 2 1 4 2 2 3 Application description Memory allocation First of all all the memory used by the module must be allocated The static parameters structure and dynamic parameters structure
6. 1 for mono 2 for stereo nb bytes per Sample int32_t Dynamic data in number of bytes 2 for 16 bit data data_ptr Pointer to data buffer must be allocated by the main framework int32_t Number of samples per channel in the data buffer int32_t Buffer mode O not interleaved 1 interleaved 2 2 2 Returned error values Possible returned error values are described below Table 11 Returned error values OMNI2 ERROR NONE O OK No error detected OMNI2 ERROR 4 Could be a bad sampling frequency or a bad a dynamic memory allocation JOMNIZ_ERROR_PARSE_COMMAND ERROR PARSE COMMAND apad LL Internal error covers bad internal settings OMNI2 BAD HW May happen if the library is not used with the right hardware 2 3 Static parameters structure Some static parameters must be set before calling the processing routine struct omni2 static param ine a 0 Omni2CentreOutput int32 t AudioMode INC32 C SamplingFreq Fi typedef struct omni2 static param omni2_static_param_t DoclD025072 Rev 4 13 26 3 Module Interfaces UM1655 Table 12 Static parameters structure ame me eet Omni2CentreOutput int32_t O to disable the center output for 3 0 1 to enable the center output 3 0 Can be one field of the eAcMode Supported enumeration described below it AudioMode int32 t is used to describe the input data format SamplingFreq int32 t I O sampling frequency in Hz The audio modes available are described be
7. 6 omni Cele alan sasea n ag nb ok eee WG HINALA wae ee Bae hie ap ere Naal mia eee Hee e 11 Table 7 OMMMIZ SCS ONO as desks bo dem a ark See SS Bar Gre ww ord Bos NG SR KA 11 Table 8 OMNIZ EUG ONG sara ae eran wenn a WG a ac we de He deren da iwc a ae a NG AGA aC nels 12 Table 9 OMMNIZ DOCES S asma bau oa ae Sen Shh oe SERS RES SER eee eas 12 Table 10 Input and output buffers eee nas 13 Table 11 Returned error values ee ee ee eee 13 Table 12 Static parameters structure eee ee eee 14 Table 13 Dynamic parameters structure 0 0 0 0 ee ee eee 15 Table 14 Setup examples eee eee nas 18 Table 15 Virtualized sound compliant with ITU T 7 1 speaker layout standards 20 Table 16 Document revision history aa 25 UM1655 List of figures List of figures Figure 1 Mono to stereo perception for mono inputs 0 0 cc ees 7 Figure 2 Stereo widening perception for stereo inputS 0 0 0 0 0 a 7 Figure 3 7 Virtualizer perception up to 7 1 Channels 0 0 00 ccc eee ees 8 Figure 4 Block diagram of the Omni2 module 2 0 0 0 ce eee 16 Figure 5 Setup for stereo widening effect 0 0 0c ee ene 18 Figure 6 Setup for multichannel virtualizer effect 0 0 a 19 Figure APICalpPrOCOQUIS 64 064 KK an ede wi Gi bee oe ad a eS a dad bd ie 23 Ky DoclD025072 Rev 4 5 26 Module overview UM1655 1 M
8. 7 26 3 Module overview UM1655 1 2 1 3 8 26 Figure 3 Virtualizer perception up to 7 1 channels Physical Speakers D Perceived Virtual Speakers a The virtualizer perception up to 7 1 channels gives the listener the impression of a multi speaker sensation with stereo speakers MS32351V1 The listening angle corresponds to the angle between the listener and the physical speakers Section 4 1 System requirements and hardware setup _LS refers to Largely Spaced speakers that is about 30 degrees listening angle _CS refers to Closely Spaced speakers that is about 20 degrees listening angle and _VCS refers to Very Closely Spaced speakers that is about 10 degrees listening angle Module configuration The module supports mono and multichannel interleaved 16 bit and 32 bit I O data up to 7 1 format lib omni2 multichannel m4 a and lib_omni2_multichannel_32b_m4 a libraries should be used for the multichannel virtualization use case while it also supports stereo widening effect Resources summary Table 2 contains the module requirements for the Flash stack and RAM memories Table 2 Resources summary Flash code Flash data Dynamic stereo text rodata RAM Omni2 for multichannel 8136 Bytes virtualization 2064 Bytes 310 Bytes 3100 Bytes 1344 Bytes Omni2 for multichannel 8130 Bytes virtualization 32 bits I O y The required core frequencies in MHz on Table 3 are measu
9. ING ANGLE 10 to have optimal effect with 10 Omni2ListeningAngle degrees listening angle OMN12 LISTENING ANGLE 20 to have optimal effect with 20 degrees listening angle and OMN12 LISTENING ANGLE 30 to have optimal effect with 30 degrees listening angle DocID025072 Rev 4 15 26 3 Algorithm description UM1655 3 Algorithm description 3 1 Processing steps The block diagram of the Omni2 module is described in Figure 4 Figure 4 Block diagram of the Omni2 module Speaker mode Speaker L Not mono adjustment filter _ No CA q M2S mode Virtualization processing Routing Speaker mode Speaker adjustment filter Mono to stereo expansion NG gt M2S mode Not mono MS32352V1 Routing block Carries out a premixing of the channels so that it can be processed with a single virtualization structure Virtualization block Applies the HRTF and Crosstalk cancellation function Speaker adjustment filter Processes the audio signal after virtualization processing for speaker rendering and spectrum preservation Mono to stereo block Carries out a mono to stereo expansion and bypasses the speaker rendering block 3 2 Data formats The module supports fixed point data in Q15 or Q31 format with a mono or a multichannel up to 7 1 interleaved pattern 2 16 26 DoclD025072 Rev 4 UM1655 3 3 Note 3 Algor
10. are exported in the omni2 glo h file so that the memory for these structures can be allocated as written in the example below Omni2 static and dynamic parameters structures memory allocation omni12 static param t static param ptr malloc sizeof omni2_static_ param_t omni2 dynamic param t dynamic param ptr malloc sizeof omni2_dynamic_ param_t Where static_param_ptr pointer is used by omni2_setParam and omni2_getParam routines dynamic param ptr pointer is used by omni2 setConfig and omni2 getConfig routines Next the static and dynamic memory required by the module must be allocated by the framework Structures are hidden to the audio framework but their sizes are exported as a constant in the omni2 glo h file so that the memory allocation can be done as written below Omni2 memory structure memory allocation void static mem ptr malloc omni2 static mem size void dynamic mem ptr malloc omni2 dynamic mem size Where e dynamic mem ptr pointer is a parameter of the omni2 reset routine e static mem ptr pointer is a parameter of all exported APIs Then it is necessary to allocate the memory for the input and output audio buffers Module API calls Once the memory as been allocated the omni2 reset routine must be called to initialize the module s static memory The omni2 reset routine must be called each time the audio processing has been stopped and started The omni2
11. at any time to process each frame int32_t omni2_process buffer_t input buffer buffer t output buffer void static mem ptr Table 9 omni2 process io ww OT es input buffer Pointer to input buffer structure Output output buffer Pointer to output buffer structure static mem ptr void i Pointer to internal static memory to internal static Pointer to internal static memory value This process routine can run in place only in case of w x to y z with w x 2 y z For instance processing such as the stereo widening effect 2 0 to 2 0 or 5 1 virtualization effect 5 1 to 2 0 can run in place 2 2 External definitions and types For genericity reasons and to facilitate the integration in the main frameworks some types and definitions have been defined 2 2 1 Input and output buffers The library is using extended I O buffers which contain in addition to the samples some useful information on the stream such as the number of channels the number of bytes per sample and the interleaving mode An I O buffer structure type as described below must be followed and filled in by the main framework before each call to the processing routine 12 26 DoclD025072 Rev 4 Kyy UM1655 Module Interfaces typedef struct int32_t nb channels int32 E nb_bytes_per_Sample void data_ptr int3z2 buffer_size int32_t mode buffer_t Table 10 Input and output buffers name CIN int32_t Number of channels in data
12. em ptr At each new frame the input buffer structure fields must be filled in as in the example below as well as the data address for the output buffer structure Then the omni2 process routine can be called Omn12 input butter configuration and processing all input_buffer_t data_ptr input buffer ptr input buffer t buffer size input buffer size input buffer t mode INTERLEAVED input buffer t nb bytes per Sample 2 input buffer t nb chamels 6 Output buffer t data ptr output butter bir output buffer t buffer size input buffer size output buffer t mode INTERLEAVED output bufter t nb bvtes per Sample 2 output buffer t nb channels 2 error omni2 process k4omni2 input buffer t sgomni2 output buffer t omni2 static mem ptr DoclD025072 Rev 4 2 UM1655 Application description 4 2 3 Module integration summary Figure 7 API call procedure Memory allocation omni2_reset static_param initialization omni2_setParam audio stream read input_buffer preparation omni2_setConfig omni2_process Audio stream write Memory freeing MS32200V 1 1 As explained above the module s static and dynamic structures have to be allocated as well as the input and output buffer according to the structures defined in Section 2 2 1 Input and output buffers Once the memory has been allocated the call to omni2_reset function initializes the internal variables 3 The module
13. getParam routine can be called while the run time process has not started to extract the current static parameters used if needed The static parameters can be set as soon as the input sampling frequency and the stream information are known The omni2 setParam routine must be called to configure the module s internal memory with the corresponding sampling frequencies and the audio mode as in the example below Omni2 static parameters setting omni2 static_param Omni2CentreOutput 0 center output disabled omni2 static_param SamplingFregq 48000 I O sampling frequency omni2 static _param AudioMode AMODE32_LFE 5 1 gt 2 0 5 1 virtualization error omni2_setParam omn12_static_param omni2 static mem ptr DocID025072 Rev 4 21 26 Application description UM1655 22 26 Now that the hardware has been configured and the module has been initialized and configured the run time processing can start Every time the dynamic parameters change they are taken into account by the module thanks to the omni2_setConfig routine Omni2 dynamic parameters setting omni2 dynamic _param Omni2Enable Omni2CtrlStruct gt Omni2Enable pa O disable 1 enable omni12_dynamic_param Omni2Strength Omni2Ctr1Struct gt Omn12Strength 5 value from 0 to 100 omni2_dynamic_param Omni2ListeningAngle Omni2Ctr1Struct gt Omni2ListeningAngle error omni2_setConfig amp omni2_dynamic_param omni2 static m
14. ithm description Performance assessment There is no objective measurement available for this module performances are only based on a subjective assessment Below a list of subjective indicators that could be used to evaluate the effect quality Balance between Left Front and Right Front capacity not to change energy on one front channel as compared to the other Balance between Left Surround and Right Surround capacity not to change energy on one surround channel as compared to the other Stereo Widening ability to increase the audio perception angle to widen the stereo signal Distinction between front and side surround channels Center image stability ability to keep the center image at the center loudspeaker or between the left and right front loudspeakers Sensitivity to sweet spot ability to feel a widening or surround effect moving away from the sweet spot described in Section 4 1 1 and Section 4 1 2 Spectrum preservation ability to keep the original spectrum perception wherever the virtual sound comes from For more information on the performance refer to Section 4 1 System requirements and hardware setup and Section 5 How to run and tune the application DocID025072 Rev 4 17 26 Application description UM1655 4 4 1 4 1 1 18 26 Application description System requirements and hardware setup The library is built to run on a Cortex M4 core without FPU usage It was integrated and validated on
15. low enum eAcMode_Supported AMODE20t 0x0 Stereo channels for dolby pro logic AMODE10 0x1 Mono channel 1 0 AMODE20 0x2 Stereo channels 2 0 AMODE30 0x3 Stereo Center channel 3 0 AMODE32 Ox7 Stereo Center channel Surround Channels 5 0 AMODE34 OxB Stereo Center channel Surround Channels Center Surround Channels 7 0 AMODE20t_LFE 0x80 Stereo channels for dolby pro logic LFE channel AMODE20_LFE Ox82 Stereo LFE channel 2 1 AMODE30_LFE 0x83 Stereo Center channel LFE channel 3 1 AMODE32 LFE Ox87 Stereo Center channel LFE channel Surround Channels 5 1 AMODE34 LFE 0x8B Stereo Center channel LFE channel Surround Channels Center Surround Channels 7 1 AMODE_ID OxFF End of supported configurations k5 2 4 Dynamic parameters structure Three dynamic parameters can be used struct omni2 dynamic param int32 t Omni2Enable int32_t Omni2Strength INC 32 E Omni2ListenigAngle y typedef struct omni2 dynamic param omni2_dynamic_param_t 2 14 26 DoclD025072 Rev 4 UM1655 Module Interfaces Table 13 Dynamic parameters structure name pve e Omni2Enable int32_t 1 to enable the effect O to disable the effect Used to widen front signals from multichannel and stereo inputs The value Omni2Strength is from 0 no widening perception to 100 maximum widening perception Can be OMNI2_LISTEN
16. nal dynamic memory This routine must be called at least once at initialization time when the real time processing has not started omni2 setParam function This procedure writes module static parameters from the main framework to the module s internal memory It can be called after the reset routine and before the start of the real time processing It handles the static parameters i e the parameters with the values which cannot be changed during the module processing frame by frame int32_t omni2 setParam omni2 static param t input static param ptr void stat1c_ mem ptr 2 DoclD025072 Rev 4 UM1655 Module Interfaces Table 5 omni2_setParam pao meme me Testo A Pointer to static parameters Input input static param ptr omni2 static param t structure static mem ptr void Pointer to internal static memory to internal static Pointer to internal static memory value T 2 1 3 omni2 getParam function This procedure gets the module static parameters from the module s internal memory to the main framework It can be called after the reset routine and before the start of the real time processing It handles the static parameters i e the parameters with values which cannot be changed during the module processing frame by frame int32_t omni2 setParam omni2 static param t input static param ptr void static mem ptr Table 6 omni2 getParam ho TU kam o es input static param ptr omni2_static_param_t P
17. odule overview 1 1 Algorithm function The module provides functions to handle mono to stereo expansion stereo widening and multichannel audio virtualization depending on the used library Table 1 describes the supported sampling rates and the input output formats depending on which library is used Table 1 Sampling rates Audio effect Channel conversions 3Upponee sampling frequencies 1 0 to 2 0 Mono2Stereo 1 0 to 3 0 2 0 center 2510 2 0 2 x to 3 0 2 0 center l l l 3 x to 2 0 lib omni2 multichannel m4 32 44 1 and 48 kHz 3 x to 3 0 2 0 center Stereo Widening Stereo Widening for 2 xt to 2 0 matrix encoded input 7441030 2 0 center 5 x to 2 0 uidchannel 5 x to 3 0 2 0 center Virtualization 7 x to 2 0 7 x to 3 0 2 0 center The module is fully functional and validated with the configurations in green in Table 1 above The figures below present the effect perception with only two physical loudspeakers 2 6 26 DoclD025072 Rev 4 UM1655 Module overview Figure 1 Mono to stereo perception for mono inputs AA A Sound image has ae Actual physical speakers much larger size if left and right Sound image has a channels are signal spot for mono decorrelated signal MS30777V1 Figure 2 Stereo widening perception for stereo inputs Actual physical speakers Perceived virtual y Perceived virtual speakers Ea A speakers MS30778V1 DocID025072 Rev 4
18. ointer to static parameters structure Input Input static mem ptr mem jstatic_mem_ptr void i Pointer to internal static memory to internal static Pointer to internal static memory value 2 1 4 omni2 setConfig function This procedure sets the module dynamic parameters from the main framework to the module internal memory It can be called at any time during the module processing after the reset and setParam routines int32_t omni2 setConf1g omni2 dynamic param t input dynamic param ptr void static mem ptr Table 7 omni2 setConfig pio tamo ype beta i e Pointer to dynamic parameters Input input_dynamic_param_ptr omni2_dynamic_param_t rs se Pointer to internal static Input static mem ptr void memory value 7 hy DoclD025072 Rev 4 11 26 Module Interfaces UM1655 2 1 5 omni2_getConfig function This procedure gets the module dynamic parameters from the internal static memory to the main framework It can be called at any time during processing after the reset and setParam routines int32_t omni2_getConfig omni2_dynamic_param_t input dynamic param ptr void static mem ptr Table 8 omni2 getConfig ao TO kam Tm bale input dynamic param ptr omni2 dynamic param t Pointer to dynamic parameters structure Input Input static mem_ ptr Pointer to internal static memory value 2 1 6 omni2_process function This procedure is the module s main processing routine It should be called
19. red on real HW running on STM32F407IG chipset with 10 ms buffers at 48 kHz DocID025072 Rev 4 Kyy UM1655 Module overview Table 3 Frequency requirements MHz Required MHz for 16 or 32 bit IO Mono2Stereo 4 8 2 0 gt 2 0 Largely Spaced Speakers 15 5 2 0 gt 2 0 Closely Spaced Speakers 17 5 2 0 gt 2 0 Very Closely Spaced Speakers 5 1 gt 2 0 Largely Spaced Speakers 25 5 5 1 gt 2 0 Closely Spaced Speakers 27 5 ooo DocID025072 Rev 4 9 26 3 Module Interfaces UM1655 2 Note 2 1 2 1 1 10 26 Module Interfaces Two files are needed to integrate this module ib_omni2_multichannel_m4 a or lib_omni2_multichannel_32b_m4 a library and the omni2_glo h header file which contains all definitions and structures to be exported to the software integration framework The audio_fw_glo h file is a generic header file common to all audio modules it must be included in the audio framework APIs Six generic functions have a software interface to the main program omni2 reset omni2_setParam omni2 getParam omni2_setConfig omni2 getConfig and omni process omni2 reset function This procedure initializes the static memory of the module and initializes static and dynamic parameters with default values int32_t omni2 reset void static mem ptr void dynamic mem ptr Table 4 omni2 reset o am e bpi OO static mem ptr Pointer to internal static memory dynamic mem ptr Pointer to inter
20. s static configuration can now be set by initializing the static_param structure once the input sampling frequency and the audio mode are known 4 Call the omni2_setParam routine to send the static parameters from the audio framework to the module 5 The audio stream is read from the proper interface and the input_buffer structure has to be filled in according to the stream characteristics number of channels sample rate interleaving and data pointer The output buffer structure has to be set as well 6 Get the dynamic parameters when they are updated and call the omni2 setConfig routine to send the dynamic parameters from the audio framework to the module Call the processing main routine to apply the effect The output audio stream can now be written in the proper interface 9 Once the processing loop is over the allocated memory has to be freed 3 DocID025072 Rev 4 23 26 How to run and tune the application UM1655 5 24 26 How to run and tune the application Once the module has been integrated into an audio framework to play samples at 48 kHz just launch the Audio player and choose a WAV or MP3 file with a 48 kHz sampling frequency if no sampling rate conversion is available The Omni2Enable from the module s dynamic parameters is used to enable and disable the effect The Omni2Strength field is used to change the virtual listening angle 0 means that virtual speakers are close to physical speakers while 10
21. some STM32F4 family devices Recommended setup for stereo widening effect The stereo widening effect is designed for 10 20 and 30 degrees typical listening angles Figure 5 Setup for stereo widening effect Physical Speakers Physical Speakers Physical Speakers Largely Spaced Speakers Closely Spaced Speakers Very Closely Spaced Speakers MSv38405V 1 Find in Jable 14 some setup examples and direct impacts on speaker distance to get a typical listening angle and an optimal stereo widening perception Table 14 Setup examples al Recommended mode to use pam fesm 9 Omne TENGAN o 2 DoclD025072 Rev 4 UM1655 Application description Table 14 Setup examples continued Inter Speaker Speaker Listener Corresponding Recommended mode foice Distance Distance Listening Angle 0 8 m 18m 25 OMNI12 LISTENING ANGLE 20 or l l OMNI2_LISTENING_ANGLE_30 It must be noted that the listener must be well centered between the two loudspeakers in order to benefit from the stereo widening effect because this effect is very sensitive to lateral sweet spot Listening angle below 20 degrees could correspond to a typical TV watching with down firing speakers small sound bars or docking stations usage Positions of the virtual front channels should vary from 15 to 50 4 1 2 Recommended setup for multichannel virtualizer effect Like the Stereo Widening effect the multichannel virtualizer effect has been designed for 10 20 and 3
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