Audio Effects - Phase Shifter
Contents
1. 6 2 6 Stage Phaser response Circuit phaser 6stage ad2 Input OdBu All Pass Corner Freq s 500Hz Low Pass Sum Filter 100 50 Anadigm 2004 Document revision 1 0 3 7th April 2004 UU dim Nat He 10kHz 10k 20k 500 Tk ZK Ak Hz Page 13 of 15 Doc No SK01FXPH U001 Audio Effects Phase Shifter APPENDIX A Alternative DC Input Interfacing Options Figure 11 gives an example of a single ended to differential converter for a single channel audio input JE C3 1 8p Je i R5 100k IL F ano VT z we Fi i socket r SB J7 Ja i be q R7 100k RB 100k ME E 5 g So oy HE VMR 1 C4 1_8p i a Ke J1 C1 1 8p J2 F he e A o R1 100k a Es ae bs ES g AA al J3 it bs sl a R3 1 00k i VMR C2 1 8p GND Figure 11 Depending on the nature of the audio signal source output drive e g if it is AC decoupled it is possible that the common mode of 2V will not be correctly established at the input using the circuit of Figure 11 An alternative is given in Figure 12 Anadigm 2004 Page 14 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 Audio Effects Phase Shifter a Ov yoo j i BY socket ot ae hf R 100k Re 4 ke 4 i R 1 100 Figure 12 Page 15 of 15 Doc No SKO1FXPH U001 Anadigm 2004 Document revision 1 0 3 7th April 20042. Audio Effects Phase Shifter Rev 1 0 3 Date 7 April 2004 Hi a 2 phaser Download Wi a i x Reset Port Simple Phaser About m Frequency sweep a ae 0 20 Hz Close Start o Log 40 00 Hz 300 00 Hz Lin Stop I Frequency HERES Anadigm 2004 Page 1 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 Audio Effects Phase Shifter TABLE OF CONTENTS PURPOSES SE a A 3 2 SETUP ce SE RE a a EF EET RIG ENE 4 2 1 BOARDS AND INTERFACE Sin nn ee nent nel tats ea eu ds eu 4 2 1 1 RPS ANO OUMU S raser re eee tn 4 2 2 SOFTWARE INSTALLATION cccececceccccececceccacececceceaceacececceaecueaeecesueaesneseeatanes 6 3 CIRCUIT DESCRIPTION cie nu 7 A CIRCUIT VARIATIONS count 8 4 1 OS TAGE PHASER Lee en sean ea caen ea den te died 8 4 2 STEREO 4 STAGE PHASER ccceccececcccecceccaceceaceacacecceneaceceaeeauecesneacsneaeeeanes 8 4 3 OTHER TECHNIQUES 22 catecnsccetactccdatactdndadectaaatdacssetardbaacsdsabaacsauahaacsdaciie 9 5 PHASER EXE SOFTWARE 0 id 10 5 1 EXECUTABLE Sa de 10 5 2 SOURCE CODES te sn tee a dE nl line 10 53 SOFTWARE EFFICIENCY erene did de dd a e ais dae adarei 12 PERFORMANCE a de aa bens 13 6 1 4 STAGE PHASER RESPONSE cccececceccccecccceccacececcececcecesneacenecueacsueaceaeanes 13 6 2 6 STAGE PHASER RESPONSE cceccccecccceccececcacccecceaeeucaceneccecesueaeeae
3. See Section 5 for more details Having installed the Starter Kit no further installation is necessary Simply double click on this file or invoke it from the Windows Start menu The executable phaser exe is installed automatically as part of the Starter Kit Its default location is lt Effects Phaser install dir gt phaser Application or it can be invoked from the Start menu Start gt Anadigm gt Starter Kits gt Subwoofer Conditioner gt Phaser Application This software will only operate with an AN221K04 evaluation kit connected to the PC s serial port using standard serial connector Disclaimer Anadigm does not make any warranty or representation as to the functionality or otherwise of the phaser application and all warranties implied or express are excluded to the extent permitted by applicable law Anadigm does not provide product support for this software Page 6 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 Audio Effects Phase Shifter 3 Circuit description Anadigm 2004 LOAD ORDER 1 Resource Panel Power td 24m LUT available counter available CAB 1 LK J opamp SAR cap comp CAB Z CLK 23 opamp SAR cap comp CAB 3 CLK 0 3 opamp SAR cap Comp CAB 4 Figure 4 Circuit of phaser 4stage ad2 The circuit of Figure 4 contains the components of a classic phase shifter using four identical all pass filter stages This can be increased or re
4. API C code functions are accessed by simple naming conventions In this example PH1 refers to the user allocated name of the FPAA device in AnadigmDesigner 2 AP nf refers to the user allocated instance name of each respective all pass FilterBilinear CAM The underlying C code function is an_setFilterAllPass an_CAM nCAM double Fo Anadigm 2004 Page 11 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 Audio Effects Phase Shifter The setFilters function is invoked from another function UpdateSampleControls Figure 9 which manages the synchronization of the user interface dialog and the settings of the physical filters This function synchronises all dialog controls and issues an update to the filters in the phaser to the current setting oe rf This ia the only place where setfilters is called LA void phaserDlg UpdateSanpletontrolst Figure 9 The UpdateSampleControls function is in turn invoked from another function OnStart Figure 10 which contains all the timing and frequency co ordination for the phaser Sm nn oe Starts the phaser sweep cycle amp checks for messages as it goes ee void phaserDlg OnStartt i Figure 10 Using this method a high degree of flexibility is easily added to the code s may be evident no optimization of the code has been performed for processor speed memory utilization or elegance 5 3 Software Efficiency The softw
5. C class library functions and makes simple Windows based controllers a breeze to create CF See AnadigmDesigner 2 in tool help information for more details on C code APIs under the Dynamic Configuration feature Additionally details on the use and features of AnadigmDesigner 2 s Visual C Prototyper tool are fully described in the AnadigmDesigner amp 2 in tool help information and in a separate purpose built Starter Kit The latter is shortly to be released on the Customer Support pages on Anadigm s website www anadigm com A brief mention will be made here of the construction of the key elements in the phaser code as a guide to the reader The main class library in which all customizations were made is called phaserDig The three functions of particular interest in this class relate to the dynamic reconfiguration of the all pass FilterBilinear CAMs and the sweeping of their pole frequencies This function is called by HFC when the main dialog ef edit controls are changed ae void phaserDlg setFilters double treq i ef reconfigure the all pas biquad m Ph1 4P1 setFilter llPas ffreg m_Phl AP 2 setFilter llPas freg m Ph1l 4P3 setFilter llPas fftregq m Ph1 4P4 setFilter llPas ffreg tT Phil EeecuteReconftigt i F Figure 8 Figure 8 shows the function setFilters which reconfigures all the FilterBilinear CAMs pole frequencies The structure of the C code wrappers is such that the respective CAMs
6. Close Start o Log 40 00 H 200 00 H i Lin i Stop I qeda Frequency 1 Figure 7 Press Port to select the serial port to which the evaluation board is connected First a configuration should be loaded to the device This is done by pressing Download The main control is the Frequency slider The range settings for this control are user selectable and are entered in the Edit boxes provided The slider can be manually adjusted or can be put into free run mode by pressing Start The rate of the sweep is set by the Rate slider or Edit box 5 2 Source Code This Starter Kit includes all the source code for Microsoft Visual C 6 0 to generate the phaser exe executable This code was initially generated Anadigm 2004 Page 10 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 Audio Effects Phase Shifter using the Visual C Prototyper tool within AnadigmDesigner amp 2 and then customized AnadigmDesigner 2 automatically generates C code application programming interfaces APIs for all user selected elements in a given design These are based on a general purpose ANSI C standard for deployment to as wide a base of processor platforms as possible The Visual C Prototyper is a tool for automatically generating a software project for Microsoft Visual C targeting a Windows platform This is for rapid prototyping of software control The Prototyper wraps the API C code in
7. are control techniques described in Section 5 2 make no attempt to optimize code A practical situation may not have a Pentium class processor available for rapid algorithmic calculations from filter parameters Clearly software efficiencies can and should be applied Figure 8 is a good example where it can be seen that four successive calls are made to the same capacitor setting algorithm with the same parameter This is clearly processor inefficient when the only practical difference between the four is the address of the capacitors being programmed Furthermore this function is called repetitively for the same values as the frequency is swept up and down One example of a more sensible alternative would be to add a new function or modify the existing function an_setFilterAllPass so that instead of directly programming the FPAA it writes the capacitor values that it calculates into a vector or matrix in the code as a single pass This way the algorithm itself need only be run once for each frequency range and the sweep algorithm simply plays out pre calculated capacitor values This is far more processor efficient Anadigm 2004 Page 12 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 Audio Effects Phase Shifter 6 Performance 6 1 4 Stage Phaser response Circuit phaser 4stage ad2 Input OdBu All Pass Corner Freq s 500Hz Low Pass Sum Filter 50 100 i Tr 5k 10kHz 10k 20k
8. duced as desired The output added to the input signal generating constructive and destructive interference in the summed signal depending on phase differences between the signals A four stage design delivers two notches in the logarithmic frequency response symmetrically spaced each side of the pole frequency of the all pass filters see Section 6 1 The objective of the design is to sweep the pole frequency of the all pass filters thus sweeping these notches within the band of choice This is done using dynamic reconfiguration of the all pass filters see Section 5 The incoming signal has a gain of 15 applied to optimise for the dynamic range of the phaser circuit The output has a Linkwitz Riley 2 order low pass filter applied following the SumFilter with corner frequency of 4kHz The second stage attenuates the outgoing signal giving an overall gain of 3 0 For single ended inputs the summing stage should have both input gains 1 0 for differential inputs the gains should be 0 5 Page 7 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 Audio Effects Phase Shifter 4 Circuit Variations 4 1 6 Stage Phaser A variant of the compressor uses 6 stages instead of 4 This design is included in the Starter Kit as phaser 6stage ad2 Figure 5 See note below ANZ2 1 E04 LOAD ORDER 1 Resource Panel Power S41 24m LUT available counter available CAB 1 CLK d opamp cap Comp CAB 2 o
9. erential to single ended converter for a single channel audio output with 2V gt 0V common mode level shift jumper positions OOOO 1111 Ji J2 J3 JA A mn configured V as outputs MPLA C1 1 8p R2 100k GND ref Single Ended Signal R1 100k socket SB1 R3 100k or E dd ref test point TP1 Differentia Signal R4 100k 1 GND Figure 3 Alternatively a single ended output can be taken directly from the I1P pin though the user is reminded of the 2V DC reference used for this signal This can be adjusted using DC level shift or Series decoupling capacitor e g 1uF Gn N B If using the input arrangement described above remember to remove all jumpers J5 8 to isolate input 12x from the board components CF For more complete information on the AN221K04 evaluation board the user is referred to the user manual AN221K04 Evaluation Board User Manual click to download www anadigm com support literature library Doc No UM30900 U010 Anadigm 2004 Document revision 1 0 3 7th April 2004 Page 5 of 15 Doc No SKO1FXPH U001 Audio Effects Phase Shifter 2 2 Software installation Anadigm 2004 The Starter Kit includes a simple Windows application called phaser exe This software works in concert with the FPAA circuit design delivering real time dynamic update data to the phaser to effect the frequency sweep In this case the software is targeted at a Windows platform
10. is likely to be true However there may be a desire to build circuits which use internal analog voltage based low frequency oscillators LFOs and voltage controlled functions The Customer CAM library is a set of modules which are available in addition to the Standard release libraries These contain elements such as the xVCFilt voltage controlled bilinear filter which can substitute the all pass FilterBilinear CAMs used in this Starter Kit Anadigm is considering the implementation of an LFO CAM With these components a phase shifter that is entirely self contained within the FPAA is feasible CF Details on the availability of Customer CAMs can be seen on the Customer Support pages of Anadigm s website www anadigm com Anadigm 2004 Page 9 of 15 Document revision 1 0 3 7th April 2004 Doc No SK01FXPH U001 Audio Effects Phase Shifter 5 phaser exe Software 5 1 Executable This tool is the other half of the phaser construction lt replaces the function of a Low Frequency Oscillator LFO that might have been used in traditional all analog designs see Section 4 3 The tool contains the configuration and parameter controls for the circuit contained in phaser 4stage ad2 Install and run the phaser exe program as described in Section 2 2 When phaser exe is invoked the dialog shown in Figure 7 appears X Download WOKV ER Reset Port Simple Phaser About Frequency sweep Rate m 0 20 Hz
11. pamp er R cap comp CAB 3 opamp cap Comp CAB 4 Figure 5 Circuit of phaser 6stage ad2 The 6 stage design introduces a third notch in the frequency response at the pole frequency of the filters see Section 6 2 In this circuit output signals are attenuated by the SumFilter 4 2 Stereo 4 Stage Phaser The Starter Kit also includes an alternative design for the Subwoofer Signal Conditioner called stereo phaser 4stage ad2 Figure 6 This is basically the circuit described in Section 3 with the simple variation that for input frequencies near and above the pole frequency setting of the filters there is up to 180 degrees of phase difference between the two output channels giving a frequency dependent stereo spatial effect In this circuit output signals are attenuated by the SumFilter Anadigm 2004 Page 8 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 Audio Effects Phase Shifter 1H231E04 LOAD ORDER 1 Resource Panel Powers 1 15m LUT available counter available CAB 1 GLK J opamp cap comp CAB 2 opamp SAR cap comp CAB 3 opamp SAR cap comp CAB 4 Figure 6 Circuit of stereo phaser 4stage ad2 4 3 Other Techniques The above audio effects are based on the principle that a microprocessor of some description is available to perform the real time dynamic update of the circuit In an environment where the FPAA is being exploited to the fullest this
12. rious options It is recommended that all signalling into and out of the evaluation board be done differentially The reader is referred to the AN221K04 Evaluation Board User Manual Anadigm Document Number UM30900 U010 for full details The above user manual recommends various input and output interface circuits for ease of connection to audio sources and active speakers a For formal performance tests all measurement instrumentation should connect directly to the FPAA header pins without any additional circuitry in the signal path To interface to the device it is assumed that a OV to 2V level shift is required The simplest way to do this for audio is to build a simple subsonic filter If a differential input signal is available the designer should apply the input signal through a pair of identical capacitors connected in series with the signal to input terminal I2 as shown in Figure 1 These capacitors work with the unity gain input stage to build a high pass filter with a corner frequency using 100nF capacitors of around 10Hz matched 100nF nF caps op Figure 1 If the input signal is single ended then an alternative input arrangement is shown in Figure 2 If using this arrangement the gain of the summing filter stage should be doubled see section 3 Anadigm 2004 Page 4 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 Audio Effects Phase Shifter Figure 2 Figure 3 shows a diff
13. sneaeeneas 13 APPENDIX A ALTERNATIVE DC INPUT INTERFACING OPTIONG 14 Anadigm 2004 Page 2 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 1 Purpose Anadigm 2004 Audio Effects Phase Shifter This document describes a reference design for implementing a simple audio phase shifter using Anadigm s AN221E04 FPAA device The circuit is accompanied by a software controller which performs the frequency sweep of the phaser The implementation included in this kit uses algorithmic programming of the phaser elements and runs on a Windows platform Alternative methods can be used targeting other processor platforms which are less memory and processor intensive The 4 stage audio effect uses 2 5 CABs of an AN221E04 FPAA This document also discusses design variations which offer different design and software options to the user and provides some bench characterizations of the design These FPAA designs are included as AnadigmDesigner 2 design files as part of this Starter Kit Page 3 of 15 Document revision 1 0 3 7th April 2004 Doc No SKO1FXPH U001 Audio Effects Phase Shifter 2 Setup 2 1 Boards and interface 2 1 1 Inputs and outputs The AN221K04 development board should be connected to the PC via the serial interface amp cable provided Depending on the type of signalling involved the user may wish to make some custom modifications to the board This section recommends va
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