SBAA497B May   2021  – April 2022 PCM3120-Q1 , PCM5120-Q1 , PCM6120-Q1 , TLV320ADC3120 , TLV320ADC5120 , TLV320ADC6120

 

  1.   Trademarks
  2. 1Introduction
  3. 2Infinite Impulse Response Filters
    1. 2.1 Digital Biquad Filter
  4. 3TLV320ADCx120 and PCMx120-Q1 Digital Biquad Filters
    1. 3.1 Filter Design Using PurePath Console
      1. 3.1.1 Example Generating Programmable Biquad Coefficients Using PurePath Console
    2. 3.2 How to Generate N0, N1, N2, D1, and D2 Coefficients with a Digital Filter Design Package
    3. 3.3 Avoid Overflow Conditions
    4. 3.4 Digital Biquad Filter Allocation to Output Channel
    5. 3.5 Programmable Coefficient Registers for Digital Biquad Filters 1–6
    6. 3.6 Programmable Coefficient Registers for Digital Biquad Filters 7–12
  5. 4How to Program the Digital Biquad Filters on the TLV320ADCx120 and PCMx120-Q1
  6. 5Typical Audio Applications for Biquad Filtering
    1. 5.1 Parametric Equalizers
  7. 6Crossover Networks
  8. 7Voice Boost
  9. 8Bass Boost
  10. 9Removing 50 Hz–60 Hz Hum With Notch Filters
  11.   A Digital Filter Design Techniques
    1.     A.A Analog Filters
  12.   B Related Documentation
  13.   B Revision History

3.1 Filter Design Using PurePath Console

To facilitate the use of the Digital Biquad Filters, the PurePath™ Console includes a graphical filter design section that plots the magnitude, phase, and group delay versus frequency. This filter design also generates the coefficients through several different filter design techniques filters. Equation 3 shows the available filter design options with a short description of the filter type. In Table 3-1, the cutoff frequency refers to the frequency when the response changes by 3 dB from the pass band.

Table 3-1 PurePath™ Console Digital Biquad Filter Options
FILTER TYPEDESCRIPTION
Band PassBand-pass filter at the specified center frequency and pass-band width (filter bandwidth)
Bass ShelfSpecified gain applied at the low frequency up to the specified cutoff frequency
Equalizer (Bandwidth)Band-pass filters at the specified center frequency and pass-band width, with the specified gain
Equalizer (Q Factor)Band-pass filter at the specified center frequency and quality factor, with the specified gain. The quality factor is the center frequency divided by the pass-band width.
GainAll pass filter at the specified gain
High-Pass Butterworth 1First-order high-pass filter with specified gain, specified cutoff frequency, maximally flat pass band and stop-band response. Stop-band frequency response has a –10 dB / decade slope.
High-Pass Butterworth 2Second-order high-pass filter with specified gain, specified cutoff frequency, maximally flat pass band and stop-band response. Stop-band frequency response has a –20 dB / decade.
High-Pass Bessel 2Second-order high-pass filter with specified gain, specified cutoff frequency, maximally flat phase and constant group delay across pass band.
High-Pass Linkwitz Riley 2Second-order high-pass filter composed of a Butterworth filter with –3 dB at the cutoff frequency. When cascading a low-pass and high-pass Linkwitz Riley filters, the overall gain at the crossover frequency is 0 dB.
High-Pass Variable Q 2Second-order high-pass filter at the specified center frequency, gain, and quality factor. The quality factor is the center frequency divided by the pass-band width.
High-Pass ChebyshevHigh-pass filter with equiripple in the pass band with maximally flat response in stop band
Low-Pass Butterworth 1First-order low-pass filter with specified gain, specified cutoff frequency, maximally flat pass band and stop-band response. Stop-band frequency response has a –10 dB / decade slope.
Low-Pass Butterworth 2Second-order low-pass filter with specified gain, specified cutoff frequency, maximally flat pass band and stop-band response. Stop-band frequency response has a –20 dB / decade.
Low-Pass Bessel 2Second-order low-pass filter with specified gain, specified cutoff frequency, maximally flat group delay across pass band
Low-Pass Linkwitz Riley 2Second-order low-pass filter composed of a Butterworth filter with –3 dB at the cutoff frequency. When cascading a low-pass and high-pass Linkwitz Riley filters, the overall gain at the crossover frequency is 0 dB.
Low-Pass Variable Q 2Second-order low-pass filter at the specified center frequency, gain, and quality factor. The quality factor is the center frequency divided by the pass-band width.
Low-Pass ChebyshevLow-pass filter with equiripple in the pass band with maximally flat response in stop band
NotchBand stop filter at the specified center frequency and stop-band width (filter bandwidth)
Phase ShiftAll pass filter with 180 degree phase shift at the specified center frequency through the width given by the bandwidth
Treble ShelfSpecified gain applied at the high frequencies past the specified cutoff frequency