Audio VU meter with Extra wide Dynamic Range 69 dB using Arduino

OK, after having some fun with stereo version of the VU meter I described in my previous blog-post, now it`s time to do a serious stuff. Studio grade VU meter ! 24 steps, equallyspaced every 3 dB, covering Extra wide Dynamic Range from -63 up to +6 dB. Single (mono) channel this time, no messing around, absolute precision at the stake. Plus, it
Audio VU meter with Extra wide Dynamic Range 69 dB using Arduino - schematic

keeps absolutely Top-Flat linear frequency response from 40 Hz up to 20 kHz(*). I`m not going into details of RGB LEDs Display, which has no modification since Tears of Rainbow  project, only plates installed in one line, form a single GIGANTIC bar-graph. There are some minor changes in mixing colors data tables, but they intuitively understandable. The most important feature in this project is autoscaling. As you, probably know, Arduino has 10 bits ADC. Only it can`t process negative half-wave, and for this reason it has only 9 bits available for AC measurements. According to DSP theory, maximum dynamic range is: As input audio waveform represents anything but perfect peak-to-peak 5Vsine-wave, real dynamic range would be lower. How much In first, there is a hardware limits. OPA (NE5532), which is: but, unfortunately, isn`t rail-to-rail type. Test results show, that compression becomenoticeable (~1 dB) when not scaled magnitude approaches level about 50 dB. That is in goodagreement with observed on oscilloscope notdistorted deviation peak-to-peak 2. 5 V. Or only half of full range of 5V. And as theory says, half is one bit less, and real DR = 1. 77 + 6. 02 x 8 = 49. 93 (~50 dB). In second, audio data is processed on block  structure basis. It means, having average of the block 50 dB, doesn`t mean that there was no spikes in the sampling pull, thatobviouslywould be clipped and introduce error in the measurements results....

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