high pass in dsp

[JWoodrell]

hey guys, I am working on an audio alarm project using a VS1053 and have it nearly complete. however an issue I have run into is that the customer can play whatever sound through it thy want, but if there is too much bass in the source material it drives the little speaker so hard its just bad.

at the end of the day, I would like help/direction in how to write a DSP routine that basically fades out anything below 1kHz. not a hard cutoff, just a nice roll off. I can filter the supplied audio files i provide to them to remove this information, but I would like to have the 1053 just take care of it no matter what sound is put through.

thankyou

[pasi]

Hi,

Perhaps the EQ5 plugin (see http://www.vlsi.fi/en/support/software/ ... ugins.html ) would be a sufficient out-of-the-box solution for you. It allows you to configure -16dB for a band and set the frequency appropriately.

A low-pass using the application hook would be the other solution.

[JWoodrell]

So in reading how that plugin works it gave me an idea.

It tells you to set the volune intentionally low, then the plugin boosts the seperate frequency ranges back up.

Since i do have bass/treble control via the default registers i am going to do the same thing. Since the treble control has 7 * +1.5dB steps = 10.5dB boost. I am going to set the "max volume" as 21 * 0.5dB steps = 10.5dB headroom. This lets me set the BASS register to 0x7100. So it will boost everything above 1k by that 10.5 so in effect its "lowering" things under by 10.5.

My question is is that treble control a hard step or is it a roll off type modification

[pasi]

That's right, you can lower the relative level of the lower frequencies using that. The transition band isn't that narrow, but when starting at 1kHz, my guess is that it is too high.

Doesn't hurt to try though.

[JWoodrell]

I am happy with the results. I will play with the plugin for future versions, but i can ship these using the treble control.

i will end up writing my own as I also need to push the channels out in mono. Right now i am just using the "right" channel and ignoring the left but some songs play different stuff through left and right and sound wierd. Its a low priority but i would like to do it.

Thanks for the assistance

[Henrik]

i will end up writing my own as I also need to push the channels out in mono. Right now i am just using the "right" channel and ignoring the left but some songs play different stuff through left and right and sound wierd. Its a low priority but i would like to do it.

An easy way to get mono output is to activate differential output mode (SM_DIFF bit in register SCI_MODE), then using Left and Right instead of Ground and Right as your outputs.

Kind regards,
- Henrik