HeadPlug MKII (SR1)

Copyright (C) 2003, 2004 Paul Groke

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

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Contents:

* Description
* Settings
* Contacting the Author


Description
-----------

This is a simple DSP plugin for using the WinAmp 2.x interface, so it should
be usable with WinAmp and any other software that supports WinAmp 2.x style
DSP plugins.

It's intended to use when listening to music (or any other sound) that was
intended to playback via normal stereo speakers via headphones.
It tries to remove the over emphasis of the stereo effect and make the
'sound-stage' a little more natural.

If you can't imagine what that's supposed to sound just give it a try,
maybe you'll like it.



Settings
--------

* Crossfeed Power:

	The relative power of the lowpass-filtered crossfeed signal that's
	taken from channel A and added to channel B.
	0.0 means none, 0.5 would be 1/2 of the original (-6dB) and 1.0
	would be just as loud as the original.
	When using "Main Signal Compensation" the low frequenzies in the
	original signal from channel B will get attenuated to flatten the
	overall frequenzy-response, so setting "Crossfeed Power" > 0.5 and
	at the same time have "Main Signal Compensation" at a high value
	will effectifely swap the low-frequenzy information of channels A
	and B.
	Settings up to 0.5 should be best - maybe a little higher depending
	on the amount of "Main Signal Compensation".

* C/F Delay:

	The delay to add to the crossfeed signal before adding it the the
	other channel.
	The value is a sample-count based on 44100 Hz sampling-frequenzy.
	The value in brackets is in milliseconds.
	Values around ~0.25-0.3ms should be realistic - but it all depends
	on the distance between your ears ;)
	Note that the plugin also supports sample-frequenzies other than
	44100 Hz and that sample-count gets scaled so that the time stays
	constant although the sample-count in the dialog does not change.

	The higher you set the the more "spacy" the sound will get,
	although setting it to high may be confusing and unpleasant (not
	to mention unrealistic) when listening longer.

* C/F Treble Power:

	The amount of high-frequenzy information to leave in the crossfeed
	signal. Setting this to 0 will somewhat strengthen the stereo effect
	but has a slight negative effect on the stereo-image - at least for
	some people.
	Values between 0.1 and 0.3 should be fine.
	Setting this near to 1.0 will degrage the effect of the plugin to
	that of a simple "stereo <-> mono" control-knob found on some
	(pre)-amplifiers.

* C/F Treble Cutoff:

	The -3dB frequenzy of the lowpass-filter for the crossfeed-signal.
	Settings aroung 2500Hz should be fine.
	The higher this value is, the longer the used FIR filters get, and
	since this plugin does not use any optimizations for the filters
	(they are calculated in O(n) per input-sample where n is the filter-
	length) high values can easily eat much CPU time.

* Main Signal Compensation:

	The amount of "compensation" to apply so that the overall frequenzy-
	response get's flat again. Without any compensation (value 0.0) the
	output signal will have an up to 6dB boost in the low frequenzies
	which is generally not wanted.
	Setting to 1.0 makes the frequenze-response absolutely flat again.
	Values of 0.7 and higher usually sound good (and setting to 1.0 is
	not always the best choice - just experiment)
	See "Decomb" and "Crossfeed Power" too.

* Decomb:

	Besides the altered frequenzy-response there is another effect
	caused by the crossfeed-signal namely a "comb filter".
	Because of the phase-difference in the main signal and the
	crossfeed-signal caused by the delay, some frequenzies are attenuated.
	Depending on the amount of crossfeed that effect can be pretty severe.
	A value of 0.0 for Decomb will do just nothing about this, and a value
	of 1.0 will compensate 100% for the comb-filter effect.
	The way the plugin does this is really damn-ass straight-forward from
	a technical point of view, but damn hard to put in words, so see the
	source-code if you want to know how it's done.

* Output Dither:

	Just on/off. On adds a little dithering to the output signal, off does
	not. The dithering is however damn simple, no noise-shaping whatsoever.

* Output Gain:

	The output amplification. All computations inside the plugin are
	done using floatingpoint numbers, so inside the plugin no clipping
	will occur. However because of the phase-differences and the added
	crossfeed-signal clipping might occur when the signal is converted back
	to 16 bit integer.
	A setting of ~0.7 should be fine as long as "Crossfeed Power" is not
	too high and "Main Signal Compensation" is not too low.
	A value of 0.5 should not lead to any clipping in the output no matter
	what the other setting are.

* Bypass:

	Just On/Off. On will bypass the entire plugin except the dither and
	output amplification part. Dither and output amplification are
	left on to make comparsion of the effect fair, since little differences
	in the overall sound-level might completely change the way the sound
	"sounds".


Contacting the Author
---------------------

Thats me, Paul Groke.

Email: paul.groke@gmx.net

Contact me if you have any questions, if you have made any additions or
changes to the software, or if you just feel like telling me about how you
like it - whatsoever.
I don't promise to answer every mail, but I probably will.


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Have fun,
have a nice day,
and walk carefully.

---

Paul Groke
