This is probably a simple question.
If I am using a graphic EQ that has no pre-amp gain control, can I just subtract the pre-amp gain from each band to achieve the same thing?
That way I am not boosting any bands, but only cutting.
Posted Jul 23, 2021, 3:04 AM UTC
Not likely, because the filters were probably calculated with a certain gain/Q assuming a 0 reference at some frequency.
Example: if your only filter was a peak of 5 dB at (say) 500 Hz, then your desired preamp gain would be -5 dB. But if you then reduced the gain of all bands by 5 dB, you're introducing a bunch of new filters to the set. With a graphic EQ,that would make your original filter flat, and you would introduce a bunch of deviations in the frequency response elsewhere because they're all bandpass filters and the result wouldn't sum to a flat response. In practice, it would probably introduce new deviations as bad or worse than what you were correcting.
Even worse, if you're using a parametric EQ, each band would provide a dip dependent on the Q of each band filter unless you calculated them carefully. This would likely introduce some ugly shapes into the response.
You might get lucky and it wouldn't mess the frequency response up too badly, but it would certainly not have the same shape as the intended EQ. Bottom line, with any sort of typical EQ curve, you're better off re-calculating the entire filter set if you can't just change the overall gain. Sorry!
Doesn't help OP but hypothetically on a parametric EQ couldn't you just add another band with an extremely large bandwidth that would act as the preamp gain
the easiest way would be to add a low-shelf filter with a very high frequency (as high as possible).
Yes, that works as well.
Do you know how I can re-calculate the filter set?
This is what I am working with:
Is it as simple as telling AutoEQ that the max gain should be 0dB rather than the default of 6dB? Or will that simply severely limit its ability to EQ to the target?
What EQ software are you using?
I'm not very familiar with AutoEQ (I generally use REW for generating correction filters) but if that's the overall gain rather than the individual filter gain it ought to work. In REW, at least, there are controls for both max overall gain and max filter gain so that you can avoid using high amplitude high Q filters (which may ring) as well as reduce the likelihood of clipping. Reducing the max individual filter gain might affect the EQ's ability to match a target, but reducing max overall gain should be able to generate an accurate curve - it does in REW at least, though it may require additional filters.
I suggest reducing max gain and generating a graph curve for the filters, then compare that to the original and verify that the shape is correct. If not, maybe someone on this sub is familiar enough with AutoEQ to suggest a better way to rebuild the filters...
Atmos App?
No, EQ settings in Plexamp app.
But I talked to the developers and am getting a proper pre-amp feature added, so the OP will be irrelevent.
Cool. Thanks for the update. I'm in a similar bind trying to apply EQ to my Xbox, via Dolby's 10-band EQ. I have a Topping DX7s, so theoretically if the pre-amp gain calls for -8.6db, leaving my DAC below that level should be clip-free, correct?
Not as far as I know.
You need to deliver a digital signal to the DAC that is lowered below full 100% level as that's what causes clipping.
If the sound source wants to use 90% of full signal, and your EQ tries to boost that by 12%, well then it will clip before even hitting the DAC, the digital signal input to the DAC will be clipped.
So you need to limit the volume level somewhere before the DAC. You need to turn down the volume in the Xbox digitally.
So you need to limit the volume level somewhere before the DAC. You need to turn down the volume in the Xbox digitally.
That's what I feared, but I'm not certain that's possible. You would think the Dolby EQ would take this into consideration.
Yes. (as far as I know)
Unfortunately No - see the other post for an explanation
Ah yes, I see it now. I failed to take into consideration the frequencies not affected by the eq... Thanks.
No
unfortunately it's not that easy.
Here's the transfer function of the individual filters, and the transfer function of all filters combined of a (random) setting on a graphic EQ:
https://imgur.com/YpF3sgv
Here's the same setting, but with -4 dB of preamp gain applied (the transfer function of all filters combined looks different, it's exactly 4 dB lower)
https://imgur.com/sJpHtf9
And for comparison, here's the transfer function of the same setting, but with -4 dB added to every filter:
https://imgur.com/uwAKQDr
It's not the same.
The reason for that is that the shape of a filter normally changes with different gain levels (unless you employ constant skirt-gain filters, but those are rather exotic, and would require different EQ settings to begin with)
Now what can you do to still achieve the main goal of using pre-amp gain: what can you do to avoid clipping?
Simple, don't turn up the volume 100 % (I'm talking about the digital volume control). This should do the trick as well.
Thanks for your detailed info.
I sort of figured it wouldn't be that simple.
I am using an iPhone app which has a standard 10-band fixed EQ. I incorrectly said Graphic EQ in my post. I don't believe that I can control the digital volume level in the iPhone as I believe the volume control controls the analog output of the amp?
Is there a way that I could re-calculate a new set of filters then that only cuts in order to get the same result?
Since all the data is available for what I am trying to do:
https://github.com/jaakkopasanen/AutoEq/tree/master/results/crinacle/harman_in-ear_2019v2/Apple%20AirPods%20Pro
I am trying to EQ Airpods Pro from Crinacle's measurements to Harman IEM 2019v2 target.
What will happen if I specify to AutoEQ a max gain of 0dB instead of the default which is 6dB. I am guessing it's not meant to work this way and wont do what I want.
Will that just severely limit AutoEQ's ability to EQ to the target?
That should work, normally the gain is controlled digitally (you don't have an analog volume control on your smartphone).