[linux-dvb] Re: Volume bug for DVB_ADAC_CRYSTAL.

[Holger Waechtler <holger@convergence.de>]

Hi,

Are Årseth wrote:
> For driver version 0.9.4 in driver/dvb.c in the function SetVolume() the 
> following code didn't work for me:
> 
>         case DVB_ADAC_CRYSTAL:
>                 volleft=127-((volleft*100)/255);
>                 volright=127-((volright*100)/255);
>                 i2c_writereg(dvb, 0x20, 0x03, volleft);
>                 i2c_writereg(dvb, 0x20, 0x04, volright);
>                 return 0;
> 
> The result is that the volume out form the tv card is very low. The reason is 
> obvious since volleft/right never can reach 0. The correct way to scale 
> volleft/right must be like this:
> 
>         case DVB_ADAC_CRYSTAL:
>                 volleft=127-((volleft*127)/255);
>                 volright=127-((volright*127)/255);
>                 i2c_writereg(dvb, 0x20, 0x03, volleft);
>                 i2c_writereg(dvb, 0x20, 0x04, volright);
>                 return 0;

please use the NEWSTRUCT branch, there these issues are fixed.


> But the values 64->127 gives almost Zero volume so the volume slider in VDR 
> gets very sensitive. A better scaling is then:
> 
>         case DVB_ADAC_CRYSTAL:
>                 volleft=64-((volleft*64)/255);
>                 volright=64-((volright*64)/255);
>                 i2c_writereg(dvb, 0x20, 0x03, volleft);
>                 i2c_writereg(dvb, 0x20, 0x04, volright);
>                 return 0;
> 
> Which works very well for me :)

this problem is caused because the volume level for the ADAC is in 
linear scale while your ear feels sound pressures in a logarithmic 
scale. it's ap to the application to apply this mapping before 
submitting the ioctl. You can implement this using a simple lookup-table 
with 256 entries.

Holger



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