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I came to something a little confusing while learning EQ techniques... this might be quite simple to some of you...

20 Hz – 20 kHz (+0, -1 dB)

i read that this means the level 1kHz (1000 Hz) is taken as a reference and the response that other frequencies are determined from in terms of equalization. No frequency has a response greater than that at 1 kHz; likewise the maximum downward deviation is 1 dB – no frequency is more than 1 dB down with respect to 1 kHz.

What part of this specification indicates that the reference level is 1kHz? For example, if I go in-store and start looking at equipment what indicates this reference level?

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    I think most manufacturers would not give you specs in such precision because it would make their product less desirable. Plus it could prove quite costly to make these measurements because you need an anechoic chamber. In addition, they don't have to specify it centered on 1kHz. It just makes a lot more sense for those reading it. – Schizomorph Sep 4 '17 at 14:39
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    I also wonder if we can hear a 1dB difference in most frequencies. – Schizomorph Sep 4 '17 at 14:41
  • @Schizomorph I guess I'll just have to read it in this way. What I can tell you about your side of the question is that, yes, i do believe a 1dB difference is audible since a +6 dB change is effectively DOUBLING of level. +12dB is a quadrupling of the level and so on. I can also tell you that all of these terms fall under the study of Equalization. – Daniel Sep 5 '17 at 12:36
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    @daniel Check out the sound level comparison chart most of the way down the page here. ( www.sengpielaudio.com/calculator-levelchange.htm ) . While TECHNICALLY 6dB is double loudness, we usually say 10dB is perceived by people as twice as loud (and is 10 times the power). 20dB is perceived by people as four times as loud (100x power). 1dB is too small to tell the difference in level, however, a change in the spectrum curve of 1dB would alter the harmonic content audibly – user22688 Sep 5 '17 at 14:51
  • Thanks @Thomas that really puts things into perspective. Well said. – Daniel Sep 5 '17 at 14:56
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I don't think 1kHz plays into it at all. For an EQ, this would be total gain from input to output. If it's nominally (+0, -1dB) it means that in neutral setting the output will not exceed the input level at any frequency but will not be attenuated by more than 1dB. That's all.

If the EQ includes an explicit preamp stage, you have to subtract the nominal gain of the preamp for getting the specification.

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For a high quality preamp, the +/- spec would be the maximum deviation over the entire measured frequency range, e.g., +0/-0.1dB measured from 5.7 Hz to 20.5 kHz. And good equipment also specifies the phase shift. I'm wondering if for an EQ that +/- spec may be the difference (or maximum error) between the dialed in EQ setting and what the EQ actually produces at its output. I could understand this kind of (encoder error) with outboard EQ's like graphic EQ's with mechanical sliders. My experience has been that with mastering grade equipment (in a mastering studio) you can hear differences as small as 0.3dB - 0.5dB change in EQ at certain frequency ranges.

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