Critique My Measurement Setup (Panasonic XR57 AVR example)

[dumpingg]

I have been inspired by the many measurement-based audio equipment evaluations posted on this forum. I want to try my hand at making my own measurements. Since I don’t own an APx555 or similar test setup, I needed to use more of a DIY approach.

This is my first posting here, and I seek feedback on my approach. I am testing my Panasonic XR57 as a starting point since amirm recently posted his results and can serve as a benchmark for my effort. (ref. https://www.audiosciencereview.com/...-sa-xr57-multi-channel-receiver-review.10480/)

My test setup is the following:
Windows 10 laptop
Focusrite Solo 3rd Gen
REW EQ Software (ref. https://www.roomeqwizard.com/)
DIY Combo Test Station 4/8 Ohm Speaker Dummy Load – Voltage Divider Signal Attenuator

A few words about my DIY Combo Test Station. I am using 2 2Gang Electrical Boxes to host (from left to right):

• a pair of speaker banana jacks
• two 4 ohm 100w rated resistors controlled by a 3 way light switch to select 4 or 8 ohm connections
• Rotary Selector Attenuator Switch (based on ref https://www.akitika.com/documents/BuildingTheAttenuatorRev4.pdf)
• Attenuated output signal RCA jack

One problem I faced, is that no matter what settings in REW or adjustments with the Attenuator or gain settings on the Focusrite, I could never get a 0 dbfs signal to show up in my measurements. All of the measured signals where lower than that. I used the following settings for the REW EQ software RTA screen:

Using the above test setup I was able to make the following measurements:

• Focusrite Solo 3rd Gen background noise (no audio cables connected not even loopback)
• Panny XR57 No Tone/No Audio input background Noise test
• Panny XR57 1Khz Test Tone
• Panny XR57 250hz Test Tone
• Panny XR57 19k and 20Khz Test Tones

I do own a multimeter, but I did not make any voltage measurements with it. I set the Panny to about -25db and adjusted the attenuator selector until the Focusrite input ring light turned green. I then increased the gain on the Focusrite input till just before it turned orange to maximize the dynamic range of the measurements.

 

[dumpingg]

I should add, not shown in the setup, connected to my Windows 10 laptop I used a Behringer UCA202 TOSLINK output into the XR57 as my audio source.

 

[RayDunzl]

One problem I faced, is that no matter what settings in REW or adjustments with the Attenuator or gain settings on the Focusrite, I could never get a 0 dbfs signal to show up in my measurements.

"The gain controls have concentric tri-colour LED ‘rings’ to confirm signal level: green indicates an input level of at least -24 dBFS (i.e., ‘signal present’), the ring then turns amber at -6 dBFS to indicate that the signal is close to clipping, and finally to red at 0 dBFS (digital clipping)"

The interface won't output 0dBfs until the halo ring turns red, and, at that point, you're clipping,

Amber color starts at -6dBfs digital output.

I see a -12 peak in your examples.

If you are recording music, you need headroom for peaks. If measuring a steady tone, you should be able to hit 0dBfs (clipping) with enough voltage input and adjustment of the gain control.

Expect increased distortion from the ADC as you approach 0dBfs.

I set the Panny to about -25db and adjusted the attenuator selector until the Focusrite input ring light turned green. I then increased the gain on the Focusrite input till just before it turned orange to maximize the dynamic range of the measurements.

Well, turn the knob till you see red and back off very slightly. Then you will be near 0Dbfs.

---

Also, in REW - Preferences -> View Tab -> "Full Scale sine rms is 0dBFS" will increase the reading on the RTA when checked, otherwise, -3dBFs might be the max reading (unsure exactly)

 

[RayDunzl]

Here's an example of the ADC distortion as you approach 0dBfs in a Clarett 4 pre:

https://www.audiosciencereview.com/...able-for-measurements.7536/page-3#post-202697

 

[dumpingg]

RayDunzi, exactly the feedback I was looking for. I followed your recommendations and was able to redo the 1khz measurement. My measurement is now very close to amirm's posted measurement. I also, got my multimeter out and measured the voltage to set my test for 5watts output.

Here is the updated 1khz measurement: