Concerned About New Amp

[tjcinnamon]

Hi All,
I recently got a new 8 Channel Amp for my heights and surrounds. Outside of having a bad 3rd channel, I'm getting some periodic weird results in the RT60 graph which I don't understand.

I've also never taken measurements using the "Atmos Channel" from file method. So perhaps that's causing an issue? I've never seen this happen before though.

 

[tjcinnamon]

Here's another pic and MDAT. I just repeatedly measured the same speaker.

 

[thothsong]

There's something very wrong; the noise floor in all of your first set of measurements is 30 dB, all the way up to 20 kHz.

 

[thothsong]

Same noise floor in your second set of measurements.

 

[tjcinnamon]

There's something very wrong; the noise floor in all of your first set of measurements is 30 dB, all the way up to 20 kHz.

Where do I find the noise floor?

 

[thothsong]

Look at the Distortion graph (and change the vertical axis to SPL).

 

[tjcinnamon]

Look at the Distortion graph (and change the vertical axis to SPL).

Just looked at that. Wondering what's wrong with it? What's it supposed to look like?

 

[sam_adams]

The measurement level is fairly low, ≈ 60dB SPL. The room noise floor is between 30 dB and 40 dB SPL. Try increasing the sweep level 15 dB to 20 dB and the sweep length to 256K to improve the S/N ratio.

 

[tjcinnamon]

The measurement level is fairly low, ≈ 60dB SPL. The room noise floor is between 30 dB and 40 dB SPL. Try increasing the sweep level 15 dB to 20 dB and the sweep length to 256K to improve the S/N ratio.

The sweeps are coming from these files:

They are: "128k short 9.1.6 Atmos sweeps"

They definitely seem quiet. I'm using VLC so I can get HDMI passthrough to get it to go through Atmos.

 

[thothsong]

Do you have older measurements to compare with? Perhaps you just have a noisy environment, but in my room, noise SPL would be under 15 dB above about 1 kHz.

 

[thothsong]

You can download 256k sweeps from that post. The Atmos sweeps are unfortunately quiet, due to not being able to control the Dolby dialog normalization metadata in the tool used to create them. You'll need to turn up the master volume when using them.

 

[sam_adams]

The sweeps are coming from these files

Some mentions were made elsewhere regarding the quality of the provided sweeps in that video. @thothsong made a series of test files that were of a much better quality and were posted in a discussion here.

 

[tjcinnamon]

Now that my kids are asleep, I'll give these a shot tomorrow.

 

[thothsong]

If you run the RTA (Spectrum, No smoothing, 64k, Forever, Hann, 50%) for a minute or so in the room with the AVR turned off, to measure background noise, what does the result look like?

 

[tjcinnamon]

If you run the RTA (Spectrum, No smoothing, 64k, Forever, Hann, 50%) for a minute or so in the room with the AVR turned off, to measure background noise, what does the result look like?

There was one bump from upstairs at 70Hz

 

[tjcinnamon]

I'm trying the new sweeps with VLC, they are much quieter than what REW puts out. Any ideas?

 

[thothsong]

As I said, the Atmos sweeps unfortunately play at a much lower volume level, so you'll need to raise the master volume level to compensate.

 

[tjcinnamon]

okay, so perhaps that's the issue

 

[thothsong]

Your RTA results don't make sense to me. Here's my room ATM:

 

[tjcinnamon]

Your RTA results don't make sense to me. Here's my room ATM:
View attachment 62840

Weird! What the heck is going on in my room (or with my computer)!?!

 

[tjcinnamon]

Your RTA results don't make sense to me. Here's my room ATM:
View attachment 62840

When you play the files what media player do you use? If I use windows media player, it doesn’t come through as Atmos. Also, I’m in windows 11.

 

[thothsong]

I would guess there's a problem with your mic.

On Windows 11, Windows Media Player won't work, use Windows Media Player Legacy instead.

 

[tjcinnamon]

I'll try a different Mic. I went through an downloaded other MDATs and the noise floors looked similar though.

 

[thothsong]

Hmm, perhaps the noise floor in your mdat files is reasonable for a UMIK-1, versus the UMIK-2 I'm now using. My old UMIK-1 measurements have a higher noise floor than my UMIK-2, although still not as high as yours. But your RTA measurement still doesn't make sense to me.

 

[thothsong]

As @sam_adams indicated, there's usually less than 30 dB separation between your measured SPL levels and your noise floor, and sometimes barely 20 dB, which presumably causes the RT60 calculations to go large, as there isn't sufficient decay over time before hitting the noise floor. If your RTA measurement was somehow just a fluke, then as suggested the fix is to run the sweeps at a sufficiently high SPL.