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Hi, I have a question about PEQ in audio signal process.

Yunsik Chung
Intellectual 1150 points

Hi, i am studying audio signal process with pure path studio.

When i use multiple PEQ(IIR digital filter), the phase changed.

I know that when phase changes in feedback system, this phase difference can cause ocillation.

But i wonder what is the effect of phase changes in audio signal process.

My system is stereo and i didn't use mic.

my system's signal flow is DAC side miniDSP -> DAC -> Audio AMP -> speaker.

I wonder what phase changes in miniDSP affect overall system and sound.

Thanks,

Yun

  • 0
    TI__Mastermind 30030 points

    Hi Yun, 

    I've looped in our PPS DSP expert,  he can help answer some of your questions.

    -Steve wilson

  • 0 in reply to Steve-Wilson
    TI__Expert 6440 points

    Hi Yun,

    IIR filters can cause instability and phase-related problems if not designed properly. Stability and phase have to be analyzed carefully before using IIR filters for audio processing systems. In general, the phase deviation caused by moderate PEQ settings (i.e. not very large gains/attenuation, or very large Q etc.) do not introduce significant phase deviations and that by itself may not be audible under normal listening conditions. However phase shifts become critical in several other scenarios, like when used in stereo applications, mixing systems etc. In some case, the phase effects can be compensated by using unity-gain all-pass filters so that the phase response becomes almost linear. But I think for the playback signal flow that you have described phase effects may not be significant.

    Best Regards.

  • 0
    Genius 3945 points

    Phase shift is part of how IIR filters work. You cannot get around it.

  • 0 in reply to Diljith
    TI__Intellectual 1150 points

    Hi Dilgith,

    Thank you for your answer.

    I cannot understand 'the phase effects can be compensated by using unity-gain all-pass filters so that the phase response becomes almost linear'.

    If we use unity-gain all-pass filter, it doesn't mean that we cannot use PEQ or any effect?

    I wonder why using unity-gain all pass filters make the phase response almost linear.

    Thanks,

    Yun