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Crossfeed, Different software implementations (bs2b, rockbox)
post Apr 20 2010, 19:10
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I'm using the bs2b crossfeed plugin with foobar2000 for quite a while now and I'd like to adapt my favourite settings to the rockbox crossfeed. The parameters of the latter are very different however. bs2b has the following parameters:

- Crossfeed db (1 - 15db)
- Crossfeed hz/ms (300hz/620ms - 2000hz/90ms)

Rockbox seems to have the same parameters as the crossfeed VST from blogohl:
Ipsilateral : signal from one channel going to the corresponding (same) ear.
Contralateral : signal from one channel going to the opposite ear.
Hi Loss contra : high frequency are more attenuated by the head than lows, so attenuation value is between 0 and - 40 dB (default is - 10dB).

Now we've got three setting where bs2b has only one. I guess all three values are somehow correlated and adjusted alltogether in bs2b, but I'd really like to know in which way... It's evident from the bs2b concept page that the HF of the contralateral channel is attenuated, but I can't figure out by which amout. And what about the ipsilateral gain?
F is frequency cutoff of the Hi shelf contralateral filter : value ajustable between 500 and 2000 Hz (default is 700 Hz)
Delay is the time delay between the ipsilateral signal and the contralateral one.

In bs2b frequency cutoff and delay are correlated, which makes sense to me as both are are dependent on the virtual speaker's azimuth. Contrary to the VST however, rockbox omits the delay setting. I guess it's a fixed value. So does it even make any sense to alter the cutoff frequency here?

This post has been edited by Northpack: Apr 20 2010, 19:25
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post Apr 21 2010, 21:48
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I commited the rockbox crossfeed : design, values but not the DSP programmation itself.
We had to be carefull not to use too much DSP power to keep compatibility with all players.
So we have only one delay, fixed to 0.43ms (if I remember correctly !)
It would be a bit better to have two different delays for low and high frequencies but then other problems occur near crossover frequencies.
The ipsilateral gain is ajustable to avoid level difference when switching with/without crossfeed : because when adding some contralateral signal, the perceived level increases (and also to avoid any risk of > 0dBFS)
In the meantime, I improved the algorithm with head-fit , maybe we will implement it sometimes on rockbox rolleyes.gif
In crossfeed+Eq an in head-fit, I give the possibility to ajust some values because no setup is ideal for everybody : head circumference, position of ears, etc...vary a lot.

This post has been edited by jlohl: Apr 21 2010, 21:52

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