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PCM5242 tuning EQ cause scale decrease issue

Bing Dong
Prodigy 450 points
Other Parts Discussed in Thread: PCM5242

HI team,

I have a issue when help customer tuning EQ about PCM5242

 Issue: Add an EQ at high frequency, scale voltage(reference voltage level) of all band will decrease a lot.

For example If adding an EQ (6dB Gain,Q=1.6)at 1kHz, output voltage at this point will increase about 6dB,and there is no effect to other frequency point,

But if adding an EQ(6dB Gain,Q=1.6) at 16Khz,output voltage will only increase about 3dB,and the scale voltage of all band  will decrease.

 

This will cause if adding an EQ (Gain>0dB)at high frequency(16Khz), the output voltage at lower frequency(1Khz) will decrease.

How to solve this issue? Customer want to realize when adding an EQ at high frequency ,there is no effect to the scale (reference voltage level).

 

 

No EQ

6dB Gain,Q=1.6

 

input signal is 1khz,0.125FFS

0.9727V

EQ frequency=1k

Output voltage:1.93V

 

input signal is 16khz,0.125FFS

1.043V

EQ frequency=16K Output voltage:1.541V

 

  • 0
    TI__Mastermind 27880 points
    Hi Bing,

    I am looking into this and will get back to you when I have more information.

    Justin
  • 0 in reply to Justin Bohr
    TI__Mastermind 27880 points
    Hi Bing,

    The reason this scales is because the PCM5242 is outputting at full scale and if you are trying to add gain to its full scale output it cant physically output a higher amplitude signal. Therefore, it makes it so that signal will be the specified gain compared to the rest of the signal content. This means scaling the signal back in order to make the specified gain a relative gain.

    Justin
  • 0 in reply to Justin Bohr
    TI__Prodigy 450 points

    Hi Justin,

    Thanks a lot

    1. My testing condition is that the analog output voltage of PCM5242 haven't reach the full scale 4.2Vrms, no matter what the output scale is ,this question will occur,so what is the full scale you refered?

    2.  customer want to  get a absolute value,if setting +6dB at 16Khz EQ, They want to get the +6dB Gain tested at AP ,not a relative vaule.  I have tried to increase the Q value of 16Khz EQ, It works,but customer don't want to modify Q, do you have any comments?

  • 0 in reply to Justin Bohr
    TI__Prodigy 450 points

    Hi Justin,

    Thanks a lot

    1. My testing condition is that the analog output voltage of PCM5242 haven't reach the full scale 4.2Vrms, no matter what the output analog scale is ,this issue will occur,so what is the full scale you refered? Is it the digital full volume of miniDSP or some one else?

    2.  customer want to  get a absolute value,if setting +6dB at 16Khz EQ, They want to get the +6dB Gain tested at AP ,not a relative vaule.  I have tried to increase the Q value of 16Khz EQ, It works,but customer don't want to modify Q, do you have any comments?