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Question about Biquad function



		

			

									
						BNewhall
					
							

			
				
									
											
							 		
		        	            							
			
			    	
			                    
                
				                on May 9, 2017 
				
			
			
		


				
		

		    		    
		    
		    	
			
Hello,
I am trying to implement a 8-pole butterworth filter on the ADSP-21479 and have a question about the biquad function provided by filter.h.

 
In the manual it states that, "For the vector versions of the biquad function, the five coefficients must be stored in the order: A2, A1, B2, B1, B0" and the number of coefficients is given as 5*sections.

 
My first question was if the coefficients need to be stored in the order 
Stage1_A2, Stage1_A1, Stage1_B2, Stage1_B1, Stage1_B0, 
Stage2_A2, Stage2_A1, Stage2_B2, Stage2_B1, Stage2_B0

 
or

 
Stage1_A2, Stage2_A2, Stage1_A1, Stage2_A1,

 
Stage1_B2, Stage2_B2, Stage1_B1, Stage2_B1,

 
Stage1_B0, Stage2_B0

 

My second question was when using Matlab to generate filter coefficients, specifically the butter function, is it valid to assume that the a and b in [b,a] = butter(n,Wn) are directly relatable to the A and B stated by the manual?

 
Thanks for your help

								


				
				
		

			
						
									
									
						
						
			
			
			
			
		


					

			





	










	

	

					



			


				
	









	
    
	

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													0
							
			
				
									
							        
            
                                    			
			                            
                        
                on May 10, 2017 4:46 AM
            
            
					
    
	
    

		
		
    
					
    Certainly it is the first answer, if you have 8-pole butterworth filter, it will be consisted of four Biquad filter. Every filter has five coffies, you must reorder the coffies as A2, A1, B2, B1, B0.  
    
 
    Also have a question, when you generate the coffies from Matlab, you put the coffies into DSP , you must minus the denominator, the coffies are -A2,-A1,B2,B1,B0
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
						
				
				
		
		
    
			
		
    
	
    

    

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