The problem with digital EQ plugins is that they upsample to do the EQ processing at a higher sample rate to avoid aliasing and other artifacts then downsample back to the input sample rate. The upsamplling/downsampling methods used are chosen for CPU efficiency and low latency rather than audiophile sound quality. That middling quality resampling is audible and lowers the sound quality compared to sending an un-EQed signal to my DAC. Even when I try EQ plugins that claim to be mastering quality linear phase they still negatively impact the sound quality. You can test this by patching in a EQ plugin, setting the EQ to flat or bypass so the EQ does no processing other than the upsampling and downsampling. Then listen to the EQ plugin patched in and patched out. Every digital EQ plugin I've tried has an audible difference between being patched in and patched out. Even when trying their highest quality linear phase options.
My DAC of choice are Schiit multibits using the super awesome linear phase combo burrito filter. That filter is the reason I use and love the Schiit multibits. When I use a digital EQ plugin the upsampling/downsampling the plugin does causes the sound quality to sound like the Schiit multibit Gungnir has been crossbred with a delta sigma DAC. And that's a crime against combo burrito filters. I didn't choose the Schiit Gungnir multibit only to end up using a digital EQ for my headphones that causes my system to sound like I'm using a middling delta sigma DAC. If I wanted a middling delta sigma sound I'd be using a $400 SMSL DAC instead.
I do use EQ to experiment with how a headphone would sound with a different frequency response profile. But I do not, and will not, use EQ for critical listening. The digital EQ does more harm than good.
+1
As for your suggested test, it should be 1db up by every slider, and then use a -1db preamp to bring it all back down. You can even use widest Q for the parametric. Problem with zero EQ is that some software detect that, and switch off! If your system has two parametric EQs, you can elevate one band by 1dB and then bring it down by the same amount using a secondary PEQ. Even with "dither" enabled, you can sometimes tell which is which. (on Jriver you can)
This brings me to an experiment that I had suggested, which
NO ONE tried, or at least no one gave any feedback on.
We all know LCD-XC 2021 is a little Bass light! our friend
@Jonne Haven routinely posts PEQ profiles for this headphone with Bass EQs of +(a lot)dB to correct this with obvious preamp reduction of the same amounts (a lot again), dictating that one may need a speaker amp to power this headphone.
Going back to my experiment, it was a simple attempt to raise the Bass by removing "one screw" from the cups on each side, to see if they heard a difference!
I even suggested it to a
famous pro reviewer. His attitude was similar to most users, " Don't bother, just EQ away!, it's easier".
But you and I know it is not.
A simple 1dB or 2dB here and there can be forgiven, but 6dB or 10dB ? and a good number of them? is not.
Putting sound quality issues aside, once you implement a +6dB bass boost, you
MUST add -6dB gain to
the whole frequency band, or you risk getting into digital overload, we all know this (actually 9dB if indeed the PEQ system uses oversampling). -6dB means, if your headphone amp had 400mW of power (most portable gear), now it has become a 100mW amp! you have lost your headroom (9dB means 50mW).
what is not so common-knowledge is that, the same does not apply to frequencies past a few hundred Hz! Why? because
Musical peaks are naturally at -6dB and more for higher frequencies, probably at -20dB for +10kHz.
I offered a simple mod. that would
Naturally/Acoustically boost the bass by up to 5.5dB, and nobody was interested!
Oh Well . . .
Here are the details of the mod. and measurements that went with it.