filter co-eff of audio code

[vikaash_kb]

Hi,

I would like to know if there are any calculations for filter co-efficients of 7 band peq , in sgtl5000.I am using to eliminate noise in the frequency band 800-3k hz

[xiangjun_rong]

Hi, Balaji,

Yes, for the codec STL5000 IC,you can set up the parameter equation via I2C interface, the PCM data cab be transferred via I2S interface. For the IIR filter coefficent, it is dependent on the center frequency, sampling frequency, band width..., you have to calculate then yourself and send the coefficent via I2C interface.

I attach the UM of STL5000, pls refer to section 7-BAND PEQ PRESET SELECTION.

Hope it can help you

BR

Xiangjun rong

[SUMANTH_M_N]

Hello

I am facing some issues with using high pass filter in SGTL codec by 7 band PEQ. that is whenever i loaded the value of specific frequency it is cutting the signal to the 1 by 3rd of that value. for example if i load for 15000hz High pass filter it is cutting the signal for 5000hz and when i set for 6000hz it is cutting the signals at 2000hz.

and i am facing this issues only with High pass filter. Is it inherently present like this feature or I am the only one facing this issue?  

[vikaash_kb]

Thanks for your help,

But I am not able to filterout the frequency range entirely, the noise still exists.

Regards,

Vikaash

[xiangjun_rong]

Hi, Vikaash,

I suppose that the IIR coefficients are inappropriate. I attach an application note about the band-pass digital filter design.

Hope it can help you

BR

Xiangjun Rong

[vikaash_kb]

thanks for your reply Rong,

I am aware of the concepts of digital and analog band pass filters and their frequency responses.Anyways your application note on the band pass filter design gave much detailing only on the formulas,My doubt is do I miss out any register setting on SGTL5000, so as to enable the peq block or some sequence in setting the registers.I have added below a pseudo code of what registers I am setting to enable peq . Please correct me if I missed out something.

DAP_CONTROL->DAP_EN = 1

DAP_PEQ->EN = 0x01

DAP_AUDIO_EQ->EN = 0x01

write the co-efficient registers for lpf of cut-off frequency 800,

DAP_FILTER_COEF_ACCESS->INDEX =0x01 

DAP_FILTER_COEF_ACCESS->WR=1

I am using this but frequencies above 800, even above 3k hz are available as I see in an equalizer application in my PC,

I suppose that the frequencies above 800 hz must be cutt  off or attenuated.But that doesnt happen.

Thanks in advance for your help.

Regards,

Vikaash

[SUMANTH_M_N]

I am also experiencing same thing, Like I set it for 1000hz cutoff LPF but I am still getting signals above that and how to overcome  this