How to determine the cause of dynamic compression

[seedragon]

I believe I'm hearing dynamic compression as I near reference levels on my system. But I'm not sure if the compression is caused by my speakers reaching their limits or the amplifiers in my AVR reaching theirs. I heard it during a few scenes of Ashoka streaming on Disney+.

Is there a way to determine which?

My 5.2.4 system comprises Revel F208 left and right with 88 dB sensitivity; Revel C208 center with 89 dB sensitivity; Revel M105 side surrounds with 86 dB sensitivity; Revel M80XC overheads with 89 dB sensitivity. They're powered by a JBL Synthesis SDR-35, which can output 120W into 8 ohms over 2 channels continuously, full spectrum, or 100W into 8 ohms over 7 channels continuously at 1khz.

Edit: My MLP is 8’ from the front channels. My room is ~4,500 cu ft.

 

[Beave]

Are you hearing compression more in the bass or in the highs? Are you hearing it from all speakers or only a certain pair or even just a single speaker? That might help narrow down the issue.

 

[Jack B]

Somewhat similar situation; not sure if I am experiencing (or hearing) dynamic range compression in the playback system, nor whether it exists (to any degree).
In playing good recordings of symphonic music, using an ATI 4003 amplifier (crossed over at 80 Hz to subwoofers) driving Revel F228Be speakers at a listening distance of 8 feet, in a 990 cubic foot room, to what degree will dynamic range compression occur, at any sane volume level? And, what’s going to crap out first, the amplifier or the speakers (or the ears)?
Your thoughtful responses/advice will be gratefully appreciated. Thanks.

 

[kemmler3D]

I believe I'm hearing dynamic compression as I near reference levels on my system. But I'm not sure if the compression is caused by my speakers reaching their limits or the amplifiers in my AVR reaching theirs. I heard it during a few scenes of Ashoka streaming on Disney+.

Is there a way to determine which?

My 5.2.4 system comprises Revel F208 left and right with 88 dB sensitivity; Revel C208 center with 89 dB sensitivity; Revel M105 side surrounds with 86 dB sensitivity; Revel M80XC overheads with 89 dB sensitivity. They're powered by a JBL Synthesis SDR-35, which can output 120W into 8 ohms over 2 channels continuously, full spectrum, or 100W into 8 ohms over 7 channels continuously at 1khz.

Edit: My MLP is 8’ from the front channels. My room is ~4,500 cu ft.

If by "reference level" you mean ~110dB then IMO (and without doing math) there's a good chance your AVR is running out of power. Your side channels are probably doing a bit of bass and that's probably taxing the overall power output considerably.

 

[DVDdoug]

if you push your amplifier or speakers past their limits you'll get clipping (distortion) and that's also dynamic compression but usually you'll notice the distortion first.

Dynamic compression (and limiting, which is a fast-kind of compression) is used in almost all audio production so most of it is in the recording, not from your playback system.

 

[Curvature]

I believe I'm hearing dynamic compression as I near reference levels on my system. But I'm not sure if the compression is caused by my speakers reaching their limits or the amplifiers in my AVR reaching theirs. I heard it during a few scenes of Ashoka streaming on Disney+.

Is there a way to determine which?

My 5.2.4 system comprises Revel F208 left and right with 88 dB sensitivity; Revel C208 center with 89 dB sensitivity; Revel M105 side surrounds with 86 dB sensitivity; Revel M80XC overheads with 89 dB sensitivity. They're powered by a JBL Synthesis SDR-35, which can output 120W into 8 ohms over 2 channels continuously, full spectrum, or 100W into 8 ohms over 7 channels continuously at 1khz.

Edit: My MLP is 8’ from the front channels. My room is ~4,500 cu ft.

Record the digital signal, analog signal before it hits the amp and acoustic playback separately at a reasonable level and at the level you hear whatever it is you hear.

Compare the peak and average magnitude of the spectrum for both levels, using the digital signal as a reference.

If you have the proper loads, you can measure the signal out of the amp.

 

[Duke]

My inclination is to suspect the speakers if you are hearing compression but not distortion, as the latter is often indicative of the onset of clipping.

Whether it's the speakers or the amp, higher efficiency speakers (with equal or better power handling) will probably solve or at least mitigate the problem. On the other hand changing amps will only solve the problem if the amp (and not the speakers) is the limiting factor.

 

[seedragon]

UPDATE: I got a new amplifier, which seems to have resolved my issue. It doesn't really make sense to me, but here's my experience.

I got a Buckeye Amps NC502MP 4-channel class-D amplifier that outputs 350 WPC into 8 Ohms. It powers my front three (LCR) channels using the SDR-35's pre-outs. I decided not to rerun Dirac Live to remove that variable from the equation. I did a listening test using my normal audio demo tracks and 4k Blu-rays at different levels, including reference (e.g., loud) level.

Result: The "dynamic compression" issue disappeared. I can crank the volume as much as I like and feel like I have essentially endless headroom. My system sounds huge.

The curious thing is that this seemed to be true at moderate volume, as well, making me wonder if the issue was insufficient power to begin with or if the amp just made my LCRs louder, which fooled my ears into thinking the dynamic compression was gone. To complicate matters further, I know that DL has had bugs in the past where filters were improperly applied in AVRs, leading to clipping and distortion at the digital level; this definitely happened to me in 2022 when I first got the SDR-35.

I have since re-run Dirac Live to factor out a simple increase in level of my front stage and got excellent results. My setup has never sounded better. Whether or not the new amplifier is responsible for the improvement or not—or whether it simply compensated for a deficiency in JBL's implementation of Dirac Live—the improvement certainly occurred after I added the amp.

Money well spent.