DIGITAL DELAY INSERTION




PROGRESSIVE DIGITAL DELAY INSERTION


Table Of Contents

1. Requirements

1.1 Introduction
1.2 Objectives
1.3 Background Theory

1.3.1 Minimum Sampling Rate
1.3.2 Silence Window and Threshold
1.3.3 Maximum Delay

1.4 Dataflow Diagram

1.4.1 DFD
1.4.2 Data Dictionary

2. Design

2.1 Block Diagram
2.2 Structure Chart
2.3 Possible Implementation Problems
2.4 References

3. Implementation

3.1 Testing

3.1.1 Test the program using FG and CRO
3.1.2 Test the program using microphone and speaker

3.2 Bench Mark and Optimisation
3.3 Problem encountered and how to overcome them
3.4 Further Improvement
3.5 Conclusion
3.6 Reference
3.7 Declaration

3.7.1 Acknowledgement

Appendix

A C50 assembly code list
B C++ host code list

1. Requirements

1.1 Introduction

PDDI ( progressive digital delay insertion ) is a digital audio device to manipulate the delay between words or silent period in a song. Delay can be progressively inserted or removed by using PDDI. The graph below shows the basic operation of PDDI.

PDDI

The application of PDDI includes:

  • Censoring the material in live talk show;
  • Sound editing ( eg shortening the time duration or lengthening it );
  • Synchronisation of video and audio.

1.2 Objectives

  • To design a PDDI controlled by the host PC which features:

  • Delay insertion ( delay is doubled )
  • Normal mode
  • Circular Buffer reset

  • To apply our Digital Signal Processing knowledge together with "C" and C50 assembler programming skills, to implement PDDI using the TMS320C50 starter's kit and observe the effects.
  • 1.3 Background Theory

    1.3.1 Minimum Sampling Rate

    Our design is mainly aiming for speech related delay insertion, the sampling rate is chosen as 8k Hz. Because the power spectrum density of human speech is concentrated below 4 k Hz bandwidth, 8 k Hz sampling rate should be sufficient to retain the speech quality. Also such sampling rate is defined by ITU-T ( former CCITT ) for toll quality telephony network.

    1.3.2 Silence Window and Threshold

    Threshold level is used to tell silence from active sound. In practical case, this is very hard to determine. The overall sound level is really controlled by the pre-amp. Therefore so as the absolute noise level. Also under different situations, the background noise level could be different. However, we can still find some meaningful value by setting everything to studio condition and measure the noise level.

    Here is a plot of a short conversation from radio:

    CHART1

    The noise level above is

    CHART2

    The threshold level for the above is 3/128 . For a 16 bits A/D, threshold will be :

                    32768*3/128 = 768.

    This way of distinguish active sound from silence is not robust as it is not able to identify strong background noise such as street noise. The most sophisticated way is to use a similar algorithm to VAD ( voice activity detection ) used in GSM. It will remove the strong background noise caused by vehicle, street noise etc by using autocorrelation method and long term filter. However, it is too complicated to implement.

    Silence window is used to determine whether it is a low sound pressure level syllabus or a real pause between words. From speech processing literature, within a frame of 10msec to 40 msec, the speech signal is usually stationary. Therefore, we can say that if it is a low sound level syllabus, it should be within 10 m sec.

    The silence window can be derived that if it is silence, it should be longer than 40 msec. With sampling rate is 8000 samples / sec, 10 msec * 8000 = 80.

    1.3.3 Maximum Delay

    The total delay time can be inserted is limited by the amount memory we can access. In our case, the total memory size is about 8 k. Therefore, the delay time will be:

                          8 K / 8 K = 1 sec.

    By using a lower sampling rate to say about 6k samples/sec, we can get 8 / 6 = 1.33 sec.

    1.4 Dataflow Diagram

    1.4.1 DFD

    DFD1

    DFD2

    DFD3

    DFD4

    1.4.2 Data Dictionary

    ISample = word
    	* Sampled analogue speech input signal *
    
    OSample = word
    	* Samples to be written to D/A chip *
    
    WinSize = word
    	* To count the number of samples below threshold *
    
    MaxWin = constant
    	* To compare with WindowSize for silence detection *
    
    UserSel = [Normal | Delay Insertion | Buffer Reset]
    
    UserInput = word
    	* Choice of UserSelection by user * 
    
    UserTmp = word
    	* The character transmitted via RS232 *
    
    receive = word
    	* The character echoed back from C50 *
    
    WinDiff = word
    	* The difference between MaxWin and WinSize *
    
    NumSample = word
    	* The number of delay samples C50 has to send *
    

    2. Design

    2.1 Block Diagram



    BLOCK DIAGRAM

    2.2 Structure Chart



    STRUCTURE CHART

    2.3 Possible Implementation Problems

    The biggest obstacle is the PC - C50 communication. Although the basic operation was demonstrated and well understood, we still don't know whether the increase of the code complexity and with RINT interrupt operating will upset the INT2 ISR.

    Also we intend to test PDDI using a microphone. In this case, the noise threshold could be much higher than the one from the radio broadcast program. This has to be solved by trial and error.

    2.4 References

    Ken C. Pohlmann, "Principles of Digital Audio", Howard W. Sams & Co., Inc., Indiana, USA, 1985.
    
    Talbot - Smith, M., "Audio Engineer's Reference Book", Butterworth-Heinemann Ltd, Great Britain, 1994.
    
    K. Blait Benson, " Audio Engineering Handbook", NewYork, McGraw-Hill, 1988
    
    Luc Baert, "Digital Audio and Compact Disc Technology", Boston, Focal Press, 1995.
    

    3. Implementation

    3.1 Testing

    The testing was done in the following two steps:

    3.1.1 Test the program using FG and CRO

    For the normal operation, the input signal is same as the output signal plus some time lagging caused by previous delay insertion.

    For the delay insertion operation, the input signal used is a DC shifted square wave with half cycle longer than silence window. The negative half cycle of the wave form is close to zero. The expected output signal should be a square wave with twice of the zero half cycle.

    SIGNAL TESTING

    The test confirmed that the negative half cycle was almost doubled.

    For buffer reset, after the user has pressed the button, any time delay caused by insertion should disappear and PDDI should go back to normal mode.

    3.1.2 Test the program using microphone and speaker

    The PC, C50, microphone and speaker are connected as below,

    MICROPHONE TESTING

    We also monitor the output of the pre amp and the output of the DSK using the CRO.

    Firstly we tested it using normal mode. No delay could be heard from the speaker.

    Then we changed it to delay insertion mode. By listening the time difference between our own voice and the sound replayed by the powered loud speaker, we can tell that delay is gradually inserted. At the maximum delay, the time difference is approximately one second. Also from the CRO, we can see the inserted signal because it is zero voltage dc.

    Finally we used circular buffer reset. After reset, there was no time delay heard and it went back to normal mode as expected.

    As summary, the testing showed that the program was working and our prediction was correct.

    3.2 Bench Mark and Optimization

    The purpose of bench mark and optimisation is mainly to see how fast these subroutines are and so to derive how fast the sampling rate can be with this set of code. The bench mark is done only on A/D interrupt service routine related code. INT2 related code is unimportant while the program is running. Although INT2 ISR will slow down the execution greatly when it is invoked, it is not continuos.

    As there are quite a few branches in the code, only the worst case ( the code executed for the longest time ) is evaluated. In our case, the longest one is as follows;

    • In Window routine, the sample is below threshold;
    • In ModeSel routine, delay insertion is selected;
    • In DelayI routine, SSamp is called;
    • In SSamp routine, it branches to ChFlag;

    The longest path in Window routine takes 21 cycles. There is one optimisation that can be made which is to use delay RETD instead of RET. It saves 2 cycles. Other branches can not be modified to delay ones as the branch only depend on the previous instruction.

    The longest path in ModeSel routine takes 13 cycles. There is no optimisation that can be made.

    The longest path in DelayI takes 20 cycles. There is no optimisation that can be made.

    The longest path in SSample takes 23 cycles. The modification can be made on the RET. It saves 2 cycles.

    Finally in RxSamp ISR, it is same for all conditions which takes 18 cycles.

    Overall without optimisation, the longest path takes 95 cycles. The maximum time is 95 * 50 nsec = 4750 nsec. The maximum sampling rate therefore is 210526 sample / sec. It is way higher than the maximum sampling rate the starter's kit can handle. After optimisation, the longest path takes 91 cycles, the maximum sampling rate is 219780. One thing need to notice is that even without any optimisation, the code execution time is more than enough. Therefore it hasn't been our primary concern.

    Finally with regarding to the overall code structure, it looks like with less CALLs and RETs the program should run much faster. However strange problems caused by INT2 forced us to use this program structure. The truth is that when the code within one subroutine is too long or branching too far, the program will crash. This program structure we adopted was the only one that wouldn't crash.

    3.3 Problems Encountered and how to overcome them

    The problems are mainly associated with INT2 operation. When PC sends a byte to C50 and causes an INT2 interrupt, the C50 program crashes. Although we still don't fully understand why it crashes under some situation, we were able to solve the problem by a lot of trial and error.

    The problem can be best described as a four tears problem.

    Firstly, we had a lot of problems to find out how to send a byte to C50 and receive one byte while not using the kernel communication program. We solved the problem by writing another function called outbyte and inbyte. It works with the sample program CHARECHO.ASM. We continued to add code related to RINT ISR into the program, but it didn't work.

    We realised that with the code we have, with RINT and INT2 both operating, the program always crashes. We tried to overcome the problem by polling RINT and using INT2 interrupt. It didn't work. We also tried polling both RINT and INT2, it worked. Actually it resulted the LAB4 we had. We thought that the problems were solved and continued on the project by adding more code.

    When the code grew in size, the program started to crash again. With the help from our tutor, we recognised that the problem was that after INT2 ISR, the IFR flag should be reset to clear the interrupt. A small program was used to test the thought and it worked. We were rather confident that the key problem was identified and there shouldn't be more trouble ahead.

    Finally, when we put the full working code into the program, it crashed again. It could be seen that the crash was caused by code size and branching range. By trial and error, we reduced the code size in each subroutine and increase the number of called functions. The final working program works perfectly. However, in some subroutine, if one more NOP is added, it will crash. We still don't know the exact cause.

    During all those attempts, we also evaluated the possibility of using source reload. Every time the user changes the mode, the program will reload the DSK code and restart the C50. It worked and the reloading process takes about 1 second. Because our project has to run in real time, this method was abandoned after all.

    3.4 Further Improvement

    • One improvement can be the implementation of PDDR ( Progressive Digital Delay Removal );
    • More external memory can be added to increase the total delay time. In C50 the total addressable memory is 64K. The maximum delay is about 8 seconds which has commercial value;
    • The window size and threshold value can be controlled by the user to adapt different situations.

    3.5 Conclusion

    The PDDI implemented using C50 Starter's kit is working as we designed. Because the way it was designed and coded, there is no trouble what so ever for real time operation. Further improvement as mentioned above can be done with more time and enough hardware support. With minor modification, this can be marketed and commercialised.

    3.6 Reference

    Borland C++ Programmer's Guide
    Borland C++ User's Guide
    TMS320C5X User's Guide
    

    3.7 Declaration

    3.7.1 Acknowledgment

    The core programs are written by the group (Louis Selvon and Bill Zeng). Some supporting subroutines are adopted and modified to suit the needs.

    The C50 assembly codes adopted are

    • AIC_INIT.ASM
    • PROCINIT.ASM

    The C50 assembly code adopted and modified is

    • PC_COMMS.ASM

    The host library is rewritten to ease the use. The main procedures are kept as they are with structure changes only. Also two other functions are added to interface with ReadByte and SendByte. For more detail, please refer to the document on C50host.

    Appendix

    A C50 assembly code list

    C50 Code list ( PROJC50.ASM )

    ; ProjC50.ASM ; This is the final version of PDDI C50 side. ; Designed by Louis Selvon and Bill Zeng ; features ; * The full working version the program ; * include ; + The normal mode operation of PDDI ( in -> out ) ; + The delay insertion mode ; * Maximum circular buffer size. ; * Circular Buffer Reset .mmregs ****** CONSTANTS SETTING ************************* ;****************************************** ;****************************************** ; AIC related constant setting ; The filter is set to about 3.4 k Hz. ; SCF = 288k * 3.6k / 3.4k = 272k which gives A => 18. ; Also sampling rate is 8 k Hz which gives B => 35. TA .set 18 ; TB .set 35 ; RA .set 18 ; RB .set 35 ; AicCtl .set 08h ; ;****************************************** ;****************************************** ; Program related constant setting CirBufH .set 0b00h ; The head of circular buffer CirBufT .set 2bffh ; The tail of circular buffer CBCtrl .set 0feh ; enable CB1 and CB2 ; AR6 is mapped to CirBuf 1 ; AR7 is mapped to CirBuf 2 ASCII1 .set 31h ; 1 in ASCII ASCII2 .set 32h ; 2 in ASCII ASCII3 .set 33h ; 3 in ASCII ZERO .set 0 ; 0 ONE .set 1 ; one MaxWin .set 80 ; The max window (default set to 10ms->80 samples) ****** DATA STARTS HERE ******** .ds 0400h Data .word 0 ; just to identify the start of data page WinSize .word 0 ; The WindowSize Thresh .word 250h ; The threshold level, default set to( 250h ) UserSel .word 0 ; The user selection from PC ; ( > 0 for delay removal ; = 0 for normal mode ; < 0 for delay insertion ) UserTmp .word 0 ; stores the user selection temperorily Sample .word 0 ; Temporary storage for the incomming sample Count .word 0 ; Use to count the number of delay samples inserted NumSamp .word 0 ; Storage of total delay samples to insert InsFlag .word 0 ; indicates whether delay insertion is on WinDiff .word 0 ; store the difference between MaxWin and WinSize ****** Setup interrupt vector *** .ps 0080ah ; start to compile from 80ah Rint: B RxSamp ; RxSamp receives sample ; from AIC and do the processing. ****** CODE STARTS HERE ******** .ps 0a00h .entry .listoff .include "procinit.asm" .include "aic_init.asm" .liston Setup: LDP #ZERO SPLK #12h,IMR ; Write to interrupt mask register ; It enables RINT and INT2 ;********************************************************* ;********************************************************* ;overwrite the INT2 vector LACC #804h ; setup destination address ; 804h is the ISR table for INT2 ; INT2 SAMM BMAR ; save to block move address register MAR *,AR0 ; point to AR0 LAR AR0,#BnchInt2 ; load source address RPT #1 ; move two words BLDP *+ ; do the move CLRC INTM ; globally enable interrupts ;**************************************************** ;**************************************************** ; Setup two circular buffers with the same memory ; location ;****************************************************** SPLK #CirBufH,CBSR1 ; load the head of circular buffer of input pointer SPLK #CirBufH,CBSR2 ; load the head of circular buffer of output pointer SPLK #CirBufT,CBER1 ; load the tail of the circular buffer of input pointer SPLK #CirBufT,CBER2 ; load the tail of the circular buffer of output pointer LACC #CirBufH ; load the head of CB SAMM AR7 ; initialise AR7 SAMM AR6 ; initialise AR6 SPLK #CBCtrl,CBCR ; load circular buffer control word ;**************************************************** ;**************************************************** ; The End of Setup Main: B Main ; wait ;**************************************************** ;**************************************************** ;**************************************************** ; Int2 receives the user's selction from PC and ; save it to UserSel. ; This ISR will also echo the selction back to PC ; for PC to check whether the right choice was ; received. ; The byte from PC is chosen as ; '1' --> 31H ; '2' --> 32H ; '3' --> 33H ; ; ISR will subtract it by 32H and make ; '1' < 0 ; '2' = 0 ; '3' > 0 ; ; By doing this, it will be easier to do branch operation ;**************************************************** ;**************************************************** Int2: CALL ReadByte ; Read one byte LDP #Data SACL UserTmp,0 CALL SendByte ; Send it back LACC UserTmp SUB #ASCII2 ; subtract the input by 32h SACL UserSel,0 ; save user input LAMM IFR AND #2h ; clear int2 interrupt SAMM IFR RETE ;************************************************* ;************************************************* ; The main operation ;************************************************* RxSamp: LAMM DRR ; read a sample LDP #Data MAR *,AR6 ; load AR6 ( CirBuf1 ) SACL *+,0 ; save the sample to CirBuf1 SACL Sample,0 ; store the sample temporily CALL Window ; call the Windowing routine CALL ModeSel ; call the mode selection routine RETE ;************************************************* ;************************************************* ; ModeSel is a subroutine to select ; which mode the user has chosen. ;*************************************************** ModeSel: LACC UserSel ; load UserSel to ACC BCND DIns,LT ; if UserSel < 0 call DelayInsertion BCND BRes,GT ; if UserSel > 0 call Buffer Reset Normal: CALL NormalM ; else UserSel = 0 call Normal mode RET DIns: CALL DelayI ; call delay insertion routine RET BRes: CALL BuffeR ; call buffer reset routine RET ;********************************************** ;********************************************** ; end of ModeSel ;****************************************************** ;****************************************************** ; Windowing ; This routine is to distinquish the noise ; from the sound by comparing the sample value ; with the threshold. ; If the sample is bigger than the threshold, ; it will reset the window size ; else it will increment the window size by one. ; ;******************************************************* ;******************************************************* Window: NOP LDP #Data LACC Sample ; load sample to ACC ABS ; take absolute value SUB Thresh ; Subtract the threshold ROL ; rotate the ACC left one bit BCND BelowT,C ; if the sample is less ; than the threshold jump ; to BelowT(hreshold) ZAP ; set ACC to zero SACL WinSize,0 ; reset WindowSize RET ; return BelowT: LACC WinSize ; load WinSize ADD #ONE ; increment by one SACL WinSize,0 ; save WinSize SACL NumSamp,1 ; save to number delay samples LACC #MaxWin ; load constant MaxWin SUB WinSize ; subtract by WinSize RETD SACL WinDiff,0 ; save the difference ;****************************************************** ;****************************************************** ; The end of Windowing ;****************************************************** ;****************************************************** ; Delay Insertion ; This routine checks whether to send delay samples ; to D/A if the windowing criteria is satisfied, or if ; more delay samples are required to be sent. ; ;******************************************************* ;******************************************************* DelayI: ZAP LDP #Data ; Set data page LACL InsFlag ; load insertion flag BCND Insert,GT ; if InsFlag is on, goes to insert ; delay LACC WinDiff ; load WinDiff ROL ; rotate left BCND Insert,C ; If WinSize >= MaxWin then proceed ; with delay insertion ; ; otherwise, do the same operation as Normal CALL NormalM RET Insert: NOP CALL SSamp ; call SSample ( SendSample ) RET ;****************************************************** ;****************************************************** ; SSample ; This routine sends delay samples to D/A ; The number of delay samples inserted is 2 * WinSize ; ;******************************************************* ;******************************************************* SSamp: ZAP ; Set ACC -> 0 SAMM DXR ; Insert delay sample LDP #Data ; set data page LACC Count ; Load counter sample -> ACC ADD #ONE ; Increment counter sample SACL Count,0 ; Save new counter sample ; check no. of delay samples inserted LACC NumSamp ; Load NumSamp -> ACC SUB Count ; Compare NumSamp with Counter sample ROL BCND ChFlag,C ; If all delay samples have been inserted ; then go to change flag LACC #ONE SACL InsFlag,0 ; else set InsFlag to one RET ; return ChFlag: LACC #ZERO SACL InsFlag,0 ; reset InsFlag SACL Count,0 ; reset count RETD SACL NumSamp,0 ; reset NumSamp ;******************************************************* ;******************************************************* ; The end of Delay Insertion ;****************************************************** ;****************************************************** ; Circular Buffer Reset ; This subroutine resets the output pointer ; ;****************************************************** ;****************************************************** BuffeR: LAMM AR6 ; read in CB1 SAMM AR7 ; write it to CB2 RET ; return ;****************************************************** ;****************************************************** ; The end of circular buffer reset ;****************************************************** ;****************************************************** ; Normal mode operation ; The output pointer ( AR7 for second circular buffer ) ; will increase by one. ; Nothing else is done ;******************************************************* ;******************************************************* NormalM: MAR *,AR7 ; setup the pointer LACC *+ ; load the output using that pointer SAMM DXR ; output RET ;****************************************************** ;****************************************************** ; The end of Normal Mode BnchInt2: B Int2 .listoff .include "pc_comms.asm" .liston .end

    B C++ host code list

    PC host code list ( PC_PROJ.CPP )

    // This program uses the // library prepared by Bill Zeng // to load PDDI into C50 // and start to execute it. #include #include "c50host.H" #define SOLID 219 // ********************************************************************** // ********************************************************************** // void ScreenSetup(void) // // It sets up the screen to accept the user input // void ScreenSetup(void) { int pos_x,pos_y; textbackground(LIGHTGRAY); textcolor(DARKGRAY); clrscr(); pos_y=2; for(pos_x=5;pos_x<=75;pos_x++) { gotoxy(pos_x,pos_y); putch(SOLID); gotoxy(pos_x,pos_y+19); putch(SOLID); }; pos_x=5; for(pos_y=2;pos_y<=20;pos_y++) { gotoxy(pos_x,pos_y); putch(SOLID); gotoxy(pos_x+70,pos_y); putch(SOLID); }; textcolor(RED); gotoxy(14,4); cprintf("P PPPPPP DDDDDDDD DDDDDDDD IIIIII"); gotoxy(14,5); cprintf(" PP PP DDDDDDDDD DDDDDDDDD II"); gotoxy(14,6); cprintf(" PP PP DD DDD DD DDD II"); gotoxy(14,7); cprintf(" PPPPPPP DD DDD DD DDD II"); gotoxy(14,8); cprintf(" PP DD DDD DD DDD II"); gotoxy(14,9); cprintf(" PP DD DDD DD DDD II"); gotoxy(14,10); cprintf(" PP DDDDDDDDD DDDDDDDDD II"); gotoxy(14,11); cprintf(" PP DDDDDDDD DDDDDDDD IIIIII"); textcolor(BLACK); gotoxy(24,13); cprintf(" by Louis, & Bill"); gotoxy(7,15); cprintf(" Choice : 1) Delay Insertion 2) Normal Mode"); gotoxy(7,16); cprintf(" 3) Buffer Rest 4) Quit"); gotoxy(7,18); textcolor(RED); cprintf("Sent selection"); gotoxy(7,19); cprintf("Received "); textbackground(LIGHTGRAY); textcolor(RED); }; void main(void) { // // set file name char appfile[50]="projc50.dsk"; // // define message char message[50]; C50Host pddi_host(appfile,1,19200,0x0a00); pddi_host.GetMessage(message); // get the message from C50Host printf(" C50 status : %s ",message); // print the message delay(1000); unsigned char UserInput; // UserInput is to be sent to C50 // it is then translated to user's selection // such as DelayInsertion // , delay removal or normal unsigned char receive; // receive stores the echo back from // c50. //******************************************************** //******************************************************** // Setup the user interface screen // ScreenSetup(); while(UserInput!='4') { delay(50); if (kbhit()) { UserInput=getch(); if ((UserInput=='1')||(UserInput=='2')||(UserInput=='3')) { gotoxy(25,18); cprintf("%c",UserInput); // send out the userinput pddi_host.outbyte(UserInput); // receive the echo receive=pddi_host.inbyte(); gotoxy(25,19); cprintf("%c HEX(%X)",receive,receive); if (UserInput=='3') { pddi_host.outbyte('2'); receive=pddi_host.inbyte(); }; }; }; // if keyboard is kit get a user input } ; }




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    PDDI ( progressive digital delay insertion ) is a digital audio device to manipulate the delay between words or silent period in a song. Delay can be progressively inserted or removed by using PDDI. To give you an idea of PDDI we'll mention snippet so you get an idea what PDDI is all about. But first you can expect our site reveals information about first processing signal a great resource with analog to dv converter that is beyond what you can imagine information provided on insert delay . Let's get started.

    The application of PDDI includes:

    As you can see a group of professionals did their research, so you'll to learn from you will learn about analog to dv converter with a state of the art resource on insert delay that no other site can match information on first processing signal .
  • To design a PDDI controlled by the host PC which features:

  • Delay insertion ( delay is doubled )
  • Normal mode
  • Circular Buffer reset

  • To apply our Digital Signal Processing knowledge together with "C" and C50 assembler programming skills, to implement PDDI using the TMS320C50 starter's kit and observe the effects.

    Our design is mainly aiming for speech related delay insertion, the sampling rate is chosen as 8k Hz. Because the power spectrum density of human speech is concentrated below 4 k Hz bandwidth, 8 k Hz sampling rate should be sufficient to retain the speech quality. Also such sampling rate is defined by ITU-T ( former CCITT ) for toll quality telephony network. So you'll be sure to learn from the site definetely delivers a resource insert delay with an excellent topic on first processing signal that sure will water your eyes the topic on analog to dv converter . Threshold level is used to tell silence from active sound. In practical case, this is very hard to determine. The overall sound level is really controlled by the pre-amp. Therefore so as the absolute noise level. Also under different situations, the background noise level could be different. However, we can still find some meaningful value by setting everything to studio condition and measure the noise level.

    This way of distinguish active sound from silence is not robust as it is not able to identify strong background noise such as street noise. The most sophisticated way is to use a similar algorithm to VAD ( voice activity detection ) used in GSM. It will remove the strong background noise caused by vehicle, street noise etc by using autocorrelation method and long term filter. However, it is too complicated to implement. Our site's content on PDDI so far gives wealth from a top notch topic on signal processing system providing a magnificent topic on analog and digital signal that sure will water your eyes the topic on delay insertion . Silence window is used to determine whether it is a low sound pressure level syllabus or a real pause between words. From speech processing literature, within a frame of 10msec to 40 msec, the speech signal is usually stationary. Therefore, we can say that if it is a low sound level syllabus, it should be within 10 m sec.

    The silence window can be derived that if it is silence, it should be longer than 40 msec. With sampling rate is 8000 samples / sec, 10 msec * 8000 = 80. Other topic provides the wealth of knowledge so you can expect our site reveals information about analog and digital signal a great resource with delay insertion that is as good as it gets with information on signal processing system . The total delay time can be inserted is limited by the amount memory we can access. In our case, the total memory size is about 8 k. Therefore, the delay time will be:

     8 K / 8 K = 1 sec.
    .

    By using a lower sampling rate to say about 6k samples/sec, we can get 8 / 6 = 1.33 sec. The biggest obstacle is the PC - C50 communication. Although the basic operation was demonstrated and well understood, we still don't know whether the increase of the code complexity and with RINT interrupt operating will upset the INT2 ISR. So you can expect our site reveals information about delay insertion with an excellent topic on signal processing system that will blow your mind on analog and digital signal . Also we intend to test PDDI using a microphone. In this case, the noise threshold could be much higher than the one from the radio broadcast program. This has to be solved by trial and error.

    For the normal operation, the input signal is same as the output signal plus some time lagging caused by previous delay insertion. So with this knowledge you will get the most spectacular site with information on first processing signal providing a magnificent topic on analog to dv converter that is as good as it gets with information on insert delay . For the delay insertion operation, the input signal used is a DC shifted square wave with half cycle longer than silence window. The negative half cycle of the wave form is close to zero. The expected output signal should be a square wave with twice of the zero half cycle.

    The test confirmed that the negative half cycle was almost doubled. For buffer reset, after the user has pressed the button, any time delay caused by insertion should disappear and PDDI should go back to normal mode. You'll get a breadth of knowlegde from you will learn about analog to dv converter a great resource with insert delay that is beyond what you can imagine information provided on first processing signal . We also monitor the output of the pre amp and the output of the DSK using the CRO.

    Firstly we tested it using normal mode. No delay could be heard from the speaker. Then we changed it to delay insertion mode. By listening the time difference between our own voice and the sound replayed by the powered loud speaker, we can tell that delay is gradually inserted. At the maximum delay, the time difference is approximately one second. Also from the CRO, we can see the inserted signal because it is zero voltage dc. Have we grabbed your attention yet. We'll don't you want knowledge from you will learn about insert delay with a state of the art resource on first processing signal that will blow your mind on analog to dv converter . Finally we used circular buffer reset. After reset, there was no time delay heard and it went back to normal mode as expected.

    As summary, the testing showed that the program was working and our prediction was correct. >The purpose of bench mark and optimisation is mainly to see how fast these subroutines are and so to derive how fast the sampling rate can be with this set of code. The bench mark is done only on A/D interrupt service routine related code. INT2 related code is unimportant while the program is running. Although INT2 ISR will slow down the execution greatly when it is invoked, it is not continuos. Now we really must have your attention. You'll sure will expect the site definetely delivers a resource signal processing system with a state of the art resource on analog and digital signal that sure will water your eyes the topic on delay insertion . As there are quite a few branches in the code, only the worst case ( the code executed for the longest time ) is evaluated. In our case, the longest one is as follows;

    So expect our site reveals information about analog and digital signal with a state of the art resource on delay insertion that will blow your mind on signal processing system . The longest path in Window routine takes 21 cycles. There is one optimisation that can be made which is to use delay RETD instead of RET. It saves 2 cycles. Other branches can not be modified to delay ones as the branch only depend on the previous instruction.

    Well we hope that what out site on PDDI has provided you with the knowledge so that you can expect a top notch topic on delay insertion with a state of the art resource on signal processing system that is beyond what you can imagine information provided on analog and digital signal . But we do not just expect you to rely on our site. To find more about PDDI why not check out those urls below :