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[bobogol]

Hello

I have a problem creating a 3 band equalization for a channel.
I want to fully isolate the 3 bands (bass, mid and high frequencies) and I also want to kill the bands one at a time.

Here is what I did so far:

// set peaking equalizer effect with no bands
HFX fxEQ=BASS_ChannelSetFX(stream, BASS_FX_BFX_PEAKEQ,0);

// create now 3 bands
float fBandwidth = 2.5; // octaves
float fCenter_Bass =    125.0f;
float fCenter_Mid  =   1000.0f;
float fCenter_Treble = 8000.0f;

BASS_BFX_PEAKEQ eq;

eq.fGain=0;
eq.fQ=0;
eq.fBandwidth=fBandwidth;
eq.lChannel=BASS_BFX_CHANALL;

// create 1st band for bass
eq.lBand=0;
eq.fGain=0;
eq.fCenter=fCenter_Bass;
BASS_FXSetParameters(fxEQ, &eq);

// create 2nd band for mid
eq.lBand=1;
eq.fGain=0;
eq.fCenter=fCenter_Mid;
BASS_FXSetParameters(fxEQ, &eq);

// create 3rd band for treble
eq.lBand=2;
eq.fGain=0;
eq.fCenter=fCenter_Treble;

BASS_FXSetParameters(fxEQ, &eq);

Did I set the bandwidth parameters correct? The bands are 3 octaves apart; fBandwidth should be 3.0 to fully isolate the 3 bands, or 1.5?

If I set -15 Db attenuation (which is the maximum value specified in the documentation) the the full kill effect isn't possible.
If I however set -50 Db attenuation for a band, the band in case gets killed but the other bands get attenuated as well (probably because I didn't isolate them properly when setting the bandwidth parameters).

Can someone offer me some hints with this? 

Thanks,
Alex

[Ian @ un4seen]

I think the problem you're experiencing there is that the bands don't end abruptly, rather they slope (roll-off) and can overlap eachother. That's why setting one band to -50 dB is also attenuating the other bands. So you should probably set the bandwidth lower than you would think, to try to compensate for that.

If you only need to kill the bands (no gain control), another thing you could try is using the BASS_FX_BFX_BQF effect to apply a high-pass filter (BASS_BFX_BQF_HIGHPASS) to kill the low band, a notch filter (BASS_BFX_BQF_NOTCH) to kill the mid band, and a low-pass filter (BASS_BFX_BQF_LOWPASS) to kill the high band.

[bobogol]

I've tried implementing a high pass filter:

    HFX fxBQF =  BASS_ChannelSetFX(chan, BASS_FX_BFX_BQF,0);

    BASS_BFX_BQF hiPass;
    hiPass.lFilter = BASS_BFX_BQF_HIGHPASS;
    hiPass.fCenter=500.0f;

    // necessary?
    hiPass.fGain=0;
    hiPass.fBandwidth=3.0f;
    hiPass.fQ=0.1f;
    hiPass.fS=0.1f;
    hiPass.lChannel = BASS_BFX_CHANALL;

    BOOL bbb = BASS_FXSetParameters(fxBQF, (void *)&hiPass);

I however get BASS_ERROR_ILLPARAM error...
Could you please help me with this! Thanks!

[Ian @ un4seen]

I think "fS" should be set to 0 when not using one of the shelving filters.

[bobogol]

Thanks a lot, that was it! 

[bobogol]

I've put together a BASS_BFX_BQF_HIGHPASS and a BASS_BFX_BQF_LOWPASS filter, both having fCenter (cut off frequency) at 750. This should mean kill all frequencies right? I can still hear sound though at higher volume level. Is there a way to attenuate more, what parameters should I tune?

[Ian @ un4seen]

As before, there is the slope/roll-off to consider; that's 12dB per octave with these filters, ie. the attenuation increases 12dB for each additional octave from the cutoff frequency (fCenter). It should be possible to increase that by adding more filters (eg. it will be 24dB/octave with 2 filters), but I'm afraid I'm not sure exactly how the parameters should be optimally set for each additional filter.

With the low/high-pass filters, I think the Q (or bandwidth) option controls resonance. In your case, you probably don't want any resonance; using fQ=0.7 should give that with a single filter, but that would probably change when using multiple filters. Note the "fBandwidth" and "fQ" options are mutually exclusive, so one or the other should be 0.