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Discussion Starter · #1 ·
https://i.imgur.com/C0qEka2.png

Pardon the incorrect graph limits, this is just the screenshot i have on hand, but any further screenshots will abide by forum guidelines.

I am attempting to EQ my car's response after a new stereo install. I put in a head unit, amplifier, front and rear speakers, and a subwoofer.

To measure, i did the following:
  • DL/install REW, plug in Dayton UMM-6 mic, load calibration file for mic
  • plugged phone into head unit aux, max volume on phone, raised volume on head unit till it was decently loud as per the graph posted. Played PINK NOISE through phone.
  • Opened RTA window in REW, hit Record button
  • move mic around multiple places in the 2 listening positions I was concerned about, saved each measurement in the RTA window
  • Took average of all measurements
  • applied 1/24 smoothing

According to wikipedia, pink noise that was generated actually is supposed to look exactly like my graph. One person said that I should be using WHITE NOISE instead if i want a flat graph. Another post I read in my search said something about REW plotting transfer functions, and that is why pink noise doesnt show up flat.

I just need someone to validate this, my methodology, and perhaps give me an alternative way to do this. I'm not trying to get a super accurate lab-grade result, i just want to have an extremely basic idea of where the peaks and dips are without having to do it by ear.

If I were to do it by ear, i'd basically play sweeps in which a guy keeps saying what frequency was just played as the sweep progresses, and then increase/decrease whatever EQ band I needed to based on that, but that is extremely tedious.
 

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According to wikipedia, pink noise that was generated actually is supposed to look exactly like my graph.
Not so. Pink noise drops 6 dB in level for each octave. That’s only 60 dB between 20-20 kHz, and your graph shows an 80 dB differential.


One person said that I should be using WHITE NOISE instead if i want a flat graph. Another post I read in my search said something about REW plotting transfer functions, and that is why pink noise doesnt show up flat.
Pink noise can indeed show up flat on a chart, if that’s what the speaker system is generating. No one uses white noise for system tuning that I’ve ever seen.


i just want to have an extremely basic idea of where the peaks and dips are without having to do it by ear.
You’ll never get an idea of where they are unless you use a graph with suitable vertical scaling.


I just need someone to validate this, my methodology, and perhaps give me an alternative way to do this. I'm not trying to get a super accurate lab-grade result
Personally I wouldn’t trust a signal from an app generated by a phone. Doesn’t your computer have an audio output?

Regards,
Wayne
 

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Discussion Starter · #3 ·
computer has an audio output but it is of far more questionable quality than my phone. i could use a test cd or use a usb flash drive to generate the tone as well.

im trying to get my usb DAC working because that actually does have a nice output, and would probably let me use REW's internal signals.

fwiw i did try the white noise and the result was still weird looking. not as drastic of a drop, but still a pretty big 30db differential along the frequency range and with huge peaks and valleys that are conveniently located where my 5 band EQ cant really do anything about them anyways.
 

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Discussion Starter · #5 · (Edited)
IT WAS DEFINITELY IN SPECTRUM MODE. YOU ARE THE WINNER!

In any case, i did end up hooking up my usb dac line out to my head unit. Set the sweep level to -35db, set my head unit volume so that the mic was also registering the same sweep level, and took a measurement.

https://imgur.com/m61DiWN

as for sorting out the sound in my car, the biggest problem was having audible bass frequencies when the windows were down, so i did a bass boost of +3 (i dunno what that translates to, its not +3db, its like a level setting) and now it seems to be pretty much perfect, if a bit too warm with the windows up.

EDIT: for educational purposes, what is the difference? or is it in the manual? if so i can just look it up there.
 

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The difference between spectrum and RTA modes is how the information is presented.

In spectrum mode the frequency content of the signal is split up into bins that are all the same width in Hz. For example, with a 64k FFT length and 48 kHz sample rate the bins are 0.732 Hz wide. The plot shows the energy in each of those bins.

In RTA mode the bin widths are an octave fraction, so their width in Hz varies with the frequency. For example, a 1 octave RTA plot has bins that are 70.7 Hz wide at 100 Hz and 707 Hz wide at 1 kHz. The plot shows the combined energy at each frequency within each bin. This is closer to how our ears perceive sound.

The different presentations mean signals with a spread of frequency content will look different on the plot. The best known examples are white noise and pink noise.

White noise has the same energy at each frequency. On a spectrum plot, which shows the energy at each frequency, the white noise plots as a horizontal line. On an RTA plot it appears as a line that rises with increasing frequency, as each RTA bin gets wider it covers more frequencies and so has more energy, the bin widths double with each doubling of frequency so the energy also doubles, which adds 3 dB on the logarithmic plots we use to show level. White noise sounds quite 'hissy', we perceive it as having more energy at higher frequencies.

Pink noise has energy that falls 3 dB with each doubling of frequency. On a spectrum plot it is a line that falls at that 3 dB per octave rate, on an RTA plot it is a horizontal line as the energy in the signal is falling at the same rate as the bins are widening. We perceive pink noise as having a uniform distribution of energy.

Single tones are a special case, they will appear at the same level on either style of plot as their energy is all at one frequency, so on a spectrum plot they show as a vertical line, on an RTA plot they show (typically) as a bar of the width of the bin width at their frequency, but the height of the bar is the same as the height of the line on the spectrum as all the energy is at that one frequency.
 
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