Eq plugin

Initial pull request for the native EQ plugin, #1376 

![image](https://cloud.githubusercontent.com/assets/7412852/5425560/4ecbfbbc-8314-11e4-9a7e-334e7910f87e.png)

On 12/25/2014 11:26 PM, Dave wrote:
>
> In plugins/Eq/EqEffect.cpp
> <https://github.com/LMMS/lmms/pull/1443#discussion-diff-22275578>:
>
> > +	const float outGain = m_eqControls.m_outGainModel.value();
> > +	const int sampleRate = Engine::mixer()->processingSampleRate() * 2;
> > +	sampleFrame m_inPeak = { 0, 0 };
> > +
> > +	if(m_eqControls.m_analyzeModel.value() )
> > +	{
> > +		m_eqControls.m_inFftBands.analyze( buf, frames );
> > +	}
> > +	else
> > +	{
> > +		m_eqControls.m_inFftBands.clear();
> > +	}
> > +	upsample( buf, frames );
> > +	gain(m_upBuf , m_upBufFrames, m_eqControls.m_inGainModel.value(), &m_inPeak );
> > +	m_eqControls.m_inPeakL = m_eqControls.m_inPeakL < m_inPeak[0] ? m_inPeak[0] : m_eqControls.m_inPeakL;
> > +	m_eqControls.m_inPeakR = m_eqControls.m_inPeakR < m_inPeak[1] ? m_inPeak[0] : m_eqControls.m_inPeakR;
>
>     I just think probably using an anti-aliasing filter is unnecessary -
>     there shouldn't be any extra >nyquist noise introduced by any of the
>     filters, and anything introduced before the EQ has already aliased and
>     thus can't be fixed by the EQ anyway...
>
>     On that note, I wonder if also the oversampling should be switchable
>     (maybe even for each filter individually?) since in biquads, it's not
>     always necessarily a desirable feature... in some cases,
>     oversampling on
>     biquads can actually be counterproductive (IIRC it can introduce more
>     noise on low cutoffs, or something).
>
> If there is not going to be a lp to remove aliasing, because there
> wont be any, is there anything gained by oversampling?
>
> sorry this is where my knowledge of oversampling stops
>

Well, it depends... it can improve accuracy for higher cutoffs, and (I
think) reduce phase shift... so maybe you could try some kind of "smart
oversampling" feature, where it's turned on only when the cutoff freq is
above a certain treshold?