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Sansa Clip Zip: EQ-settings different for each channel?

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mcc01:
Hi,

regarding the hardware of the ansa Clip ZIP: Suppose one could
implement it...would the hardware support different sound setting
(equalizer and such alike) for left and right channel?
If "Yes": Happy!
If "No": Would it be possible to do such things in software only
without frying the CPU or empty the battery in half an hour?
:)
Thank you for any help in advance !
Best regards,
mcc

saratoga:
Its not possible currently, but it would not be difficult to implement.  Right now the EQ is applied to each channel separately, but the same filter coefficients are used each time. 

See filter_process in dsp_filter.c:  http://git.rockbox.org/?p=rockbox.git;a=blob;f=lib/rbcodec/dsp/dsp_filter.c;h=b74d499e51df99ace73bdba1de59a79ddb639147;hb=HEAD

The ARM assembly version of that function is also relevant on most devices:  http://git.rockbox.org/?p=rockbox.git;a=blob;f=lib/rbcodec/dsp/dsp_arm.S;h=16394b86909571aec590eb54002b753f52647a40;hb=HEAD#l560

mcc01:
Hi Saratoga,

thanks for the good news and the pointers into the source. I have ordered a Sansa Clip Zip, which
is still on the way.
I already have compiled and installed the cross-compiler environment (I am on Gentoo Linux) and
compiled the current source code.
I only found th eprecompiled firmware of the devices...is there a Tar-ball (or something like that) of the source
of the stable release available somewhere ?

Have a nice Sunday! :)
Best regards,
mcc

saratoga:
You can check out the source code from git, however if you built the cross compiler you probably already did this.

mcc01:
Hi,

sorry for the delay...I had to get used to the make-install-boot-sequence of ROCKbox.

Since I am no audio-professional I have some questions to find the "best" way to implement
a Left/Right-aware handling of the Equalizer.

First one
In Rockbox there are quite a few Equalizers and Setting ot modify the sound. What is the
(and here it becomes complicate for me, since English is not my mother's tongue) "most
fundamental one?
Or in other words:
The simple "Treble/Bass"-Settings can easily be "emulated" by the more advanced "Graphical
Equalizer"-setting, which in turn can be emulated by...and so on.

What is the "last Equalizer"...the one, which can emulate all others?

This is the one I have to tweak first.

Second question:
I found -- and hope that it is correct -- that SELECT isn't used for the Equalizers.
I thought of an implementation like this:
The Equalizers are divided into three blocks of settings: Left, Right and Both.
"Both" is already there and means "bith channels are modified identically.
"Left" and "Right" means: Only the left of the right channel will be modified.

What to change will be selected with "SELECT". A small "left" or "right" or "both"
can be made visible on the screen.

Now...what is the best way for the following situation: Suppose one has a problems
to hear the higher freqs of the music with h(e/i)s left ear. So S/he changes the equalizer
settings for Left accordingly.
Then s/he changes the earphones. The new ones have a little to bright sound, so s/he
wants to lower the heights for both, Left and Right AND wants to keep the left-ear-related
setting from the previous settings.

S/he changes to Both with SELECT and lowers the upper freqs a little.

Is it correct to subtract the amount of dezibel on both sides even if their starting point
of the scale is different???

Thank you very much in advance for any help!
Best regards,
mcc

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