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ADSP21161 EZ-KIT Lite Slapback Demo

Analog Devices, Inc.
DSP Division
Three Technology Way
P.O. Box 9106
Norwood, MA 02062

Date Created:	8/14/01

Files contained in this directory:

21161_EZKIT_Lite.ldf			Linker Description File
MonoStereoDelay.dpj			Visual DSP++ 2.0 Project File
AD1836_reg_init_viaSPORTs.asm		Source for initializing AD1836 codec
AD1852_SPI_init.asm			Source for initializing AD1852 codec
Clear_SPT_regs.asm			Subroutines to clear SPORT1 registers
Init_21161_EZKit.asm			Source for main routine
ISR_table.asm				Interrupt Vector Table
ADT&Slapback.asm			Source file for subroutine
AUTODOUBLETRACKING&SLAPBACKDELAY.dxe	DSP Executable file
SDRAM_initialization.asm		Initialize External Memory
SPORT02_TDM_Initialization.asm		Initialize SPORTS 0 & 2
SPT0_ISR_1836_Processing.asm		Interrupt Routine for SPT0
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CONTENTS

I.	FUNCTION/ALGORITHM DESCRIPTION
II.	IMPLEMENTATION DESCRIPTION
III.	OPERATION DESCRIPTION       


I. FUNCTION/ALGORITHM DESCRIPTION

The basis of this project is the 21161 talkthrough example. A processing subroutine
is inserted into the Talkthrough routine.

II.   IMPLEMENTATION DESCRIPTION

Slapback ('Doubling') Effect (also called Mono Automatic Double Tracking)                       
One popular use of the digital delay is to quickly repeat the input signal with a single        
reflection at unity gain. By making the delay an input signal around 15-40 milliseconds,        
the resulting output produces a "slapback/doubling " effect.  The slight differences in the     
delay create the effect of the two parts being played in unison.  The effect is created by      
adding a delayed signal together with the original, where a single input source is mixed with   
the delay, and the result is sent to both output channels.  With short delays, slapback can      
thicken the sound of an instrument or voice when mixed for a mono result, although              
cancellations can occur from comb filtering side effects when the delay is under 10 ms,         
which will result in a hollow, resonant sound.  Longer slapback delay effects were commonly     
used in the 1950's/1960's music industry.                                                       
                                                                                                
                                                                                                
Mono ADT I/O Equation and Structure:                                                            
                        	y(n) = x(n) - ax(n - D)                                                 
                        	yLeft(n) = yRight(n) = y(n)                                             
                                                                                                
     x(n) ------------------------------------------|>------>O--------> y(n)                    
            |                                       1/2      ^                                  
            |                                                |                                  
            |                _______________                 |                                  
            |               |               |                |                                  
            |               |               |                |                                  
            |-------------->|     Z^(-D)    |------|>--------|                                  
                            |               |      1/2                                          
                            |_______________|                                                   
                                                                                                
                                                                                                
This effect is great for 'spicing' up an instrument or vocal track, such as compensating        
for a singer who is slightly out of key.  To truly simulate a doubling effect, some random      
delay line modulation can be added, since 2 singers are never truely in sync with one another.  

Stereo Automatic Double Tracking (Stereo Doubling) - "Concert Announcer Simulation"             *
Automatic Double Tracking, which is used by audio engineers in the music industry to create     *
a sense of spaciousness in stereophonic systems.   This effect is set up to playback the        *
original "dry" signal in one stereo channel and the delayed signal in the other channel.        *
This creates the impression of a stereo effect using a single mono source. By making the        *
delay an input signal around 15-40 milliseconds, the resulting output produces a                *
"stereo doubling" effect.                                                                       *
                                                                                                   *
                                                                                                   *
Stereo ADT I/O Equation and Structure:                                                          *
                                        yLeft(n) = x(n)                                            *
                                        yRight(n) = x(n - D)                                       *
                                                                                                   *
       x(n) --------------------------------------------------|>-----------> yLeft(n)              *
                      |                                        1/2                                 *
                      |			                                                                *
                      |             _______________                                                *
                      |            |               |                                               *
                      |            |               |                                               *
                      |----------->|     Z^(-D)    |-----------|>-----------> yRight(n)            *
                                   |               |           1/2                                 *
                                   |_______________|                                               *
                                                               


	For more introductory information, visit:
	http://www.harmony-central.com/Effects/effects-explained.html


III.  OPERATION DESCRIPTION

- Plug in a microphone to Mic In and speakers to Ch 2 (Line Out) on the 21161 Ezkit Lite
- Open the project "MonoStereoDelay.dpj" in the VisualDSP++ Integrated Development Environment (IDE).
- Under the "Project" menu, select "Build Project".
- Open a ADSP21161 EZ-KIT Lite session in the VisualDSP++ Debugger.
- Load "AUTODOUBLETRACKING&SLAPBACKDELAY.dxe"
- Run the Project and speak into the microphone and hear the generated effect.
- Use the IRQ1 and IRQ2 pushbuttons to change the effect settings.
- Pressing the FLAG3 pushbutton will bypass the audio effect.