Dolby Atmos and REW

[Michael Boeker]

Yes, but the sweeps aren't compatible with REW.

Correct, it needs AudioTools. AudioTools is the standard measurement software used by the Home Acoustics Alliance (HAA) training/certification for home theater calibration. The conversation morphed to not being able to even test channels beyond 7.1 and I am showing how it is possible with both REW and other methods. You can use the Surround Generator Dolby Atmos pink noise signals with REW for frequency response and levels.

 

[Matthew J Poes]

If you want to do more than frequency response, then in most receivers you can use the amp assign feature to assign the various height/presence channels as Zone2, Zone3, or Bi-Amp. This lets one send test signals directly through those outputs via HDMI input. This works for Denon, Marantz, Arcam, Yamaha, and many others. Once testing is done, one can revert back to the correct output setup for the room. As an example, one can send any REW test signal through all the output channels of a Yamaha RX-A3080

View attachment 51937

or Denon AVR-X3700H

View attachment 51938

You can leave the speakers connected to those channels or output to an oscilloscope, etc.

For setting distance, the Dolby Atmos pink noise test signals work just fine for measurements with SMAART's dual channel transfer function measurement and delay finder.

Ok thank you. That is definitely something I never realized was possible.

do you know if the pre-pros can reassign Atmos channels as zone 2 as well? The amps were the bigger challenge and your solution would work for that. But even measuring the noise and distortion on an audio analyzer was an issue without such a capability.

in any case, I learned something new. Thank you very much.

the Apple TV was actually the way I eventually figured out how to measure a second batch of sound bars. It’s also what I told Harman to use but I guess it didn’t meet their requirements. It’s a little tricky to use with REW. It’s sweep isn’t useable as is for doing a transfer function measurement with REW. You have to capture it as a wav and then process it manually.

 

[thothsong]

You can use the Surround Generator Dolby Atmos pink noise signals with REW for frequency response and levels.

Sure, but for full range you might as well use the free downloadable Dolby test tones instead.

 

[canavan]

If anyone is still interested in producing Atmos encoded measurement sweep files for REW, that should be relatively easy and cheap, if lossy encoding is good enough. Amazon Media Encoder can produce "channel based" 9.1.6 files where the channels beyond 7.1 are just mapped to fixed objects at default locations for those speakers. I've encoded a bunch of similar files for the Smyth Realisier, and we've found those to be good enough.

I have a bunch of bash scripts that essentially use sox, imagemagick and ffmpeg to create a mp4 video with a 16 channel audio track that can be converted with Amazon Media Encoder. I can provide the scripts and some support, if anyone with access to a 9.1.6 installation and enough time and experience with REW to validate the results would be interested in trying this out.

 

[thothsong]

If anyone is still interested in producing Atmos encoded measurement sweep files for REW, that should be relatively easy and cheap, if lossy encoding is good enough. Amazon Media Encoder can produce "channel based" 9.1.6 files where the channels beyond 7.1 are just mapped to fixed objects at default locations for those speakers. I've encoded a bunch of similar files for the Smyth Realisier, and we've found those to be good enough.

I have a bunch of bash scripts that essentially use sox, imagemagick and ffmpeg to create a mp4 video with a 16 channel audio track that can be converted with Amazon Media Encoder. I can provide the scripts and some support, if anyone with access to a 9.1.6 installation and enough time and experience with REW to validate the results would be interested in trying this out.

Cool, I'm definitely interested. (Dumb of me not to have looked at AWS before.)

 

[thothsong]

I can provide the scripts and some support, if anyone with access to a 9.1.6 installation and enough time and experience with REW to validate the results would be interested in trying this out.

It looks like I can just use AWS Elemental MediaConvert through the AWS Console, no scripting required. I'll give it a shot.

 

[canavan]

It looks like I can just use AWS Elemental MediaConvert through the AWS Console, no scripting required. I'll give it a shot.

Correct. I used the scripts to produce a matching video with title card, a simple animation which speakers are currently active etc, and to automate the re-mapping of the various channel based input files from 2.0 over 5.1 to 9.1.6 to the channel order required by AWS. I think you'll need some kind of video track to use AWS, but for testing, you can probably just take whatever you have. I've attached the json config I've used.

 

[thothsong]

I think you'll need some kind of video track to use AWS

Actually, it's easy to create audio-only mp4's.

 

[canavan]

Actually, it's easy to create audio-only mp4's.

It's easy to create them, but as far as I can tell, it's easier to find playback equipment for video+audio mp4s with Atmos than for audio only mp4s. If you can convince AWS to accept your files and play the results, that's great.

 

[thothsong]

Before I go too far down the rabbit hole, here are four files that others can test, to see if I'm on a useful track. These are audio-only mp4 measurement sweep files for height speakers (x.x.4), with timing ref in the Center channel. They are derived from an REW-generated sweep file with parameters 1M length, 20 Hz to 20 kHz, -12 dBFS, 48 kHz, 32-bit Float, so you should use those parameters to generate your local sweep file to load into REW (resulting file name is 1MMeasSweep_20_to_20000_-12_dBFS_48k_Float_L_refR.wav).

https://rew-atmos-files.s3.amazonaws.com/1M_20_to_20000_48k_Ltf.mp4

https://rew-atmos-files.s3.amazonaws.com/1M_20_to_20000_48k_Rtf.mp4

https://rew-atmos-files.s3.amazonaws.com/1M_20_to_20000_48k_Ltr.mp4

https://rew-atmos-files.s3.amazonaws.com/1M_20_to_20000_48k_Rtr.mp4

Let me know if they work for you, or if you don't like the parameters. The overall volume level is lower than what I expected, so that's something still to investigate.

Edit: these links no longer work, see later post for full download.

 

[thothsong]

For me, the files are playing about 10 dB lower than I had expected. That appears to be due to MediaConvert having a hardwired algorithm for calculating the Dolby dialnorm. Fortunately, I have my own custom DD+ Atmos parser, and I can edit the files to increase dialnorm by 10 dB, to correct that in future iterations.

 

[thothsong]

, Dolby's Atmos content protection covers all of the data, not just the Atmos metadata, so I can't alter dialnorm. May just have to live with it.

 

[canavan]

Have you tried setting Eac3AtmosDialogueIntelligence to false?

 

[thothsong]

Have you tried setting Eac3AtmosDialogueIntelligence to false?

Yep.

 

[thothsong]

OK, hopefully I've set this up right, and anyone can use this link to download a complete 9.1.6 set:

1M_20_to_20000_48k_V2.zip

Atmos 9.1.6 sweeps for REW

drive.google.com

For convenience, I've included the original REW-generated WAV file to load into REW when you take measurements. Again, these are audio-only mp4 sweeps, 1M length, 20 Hz to 20kHz, 48 kHz, with timing ref in the Center channel. For simplicity I kept the LFE file at 20 Hz to 20 kHz, even though Dolby LFE has a hard cap at 120 Hz. Let me know what you think.

 

[canavan]

I haven't even tried measuring with REW, but my preamp sometimes fails to play back the initial chirp. A bit more padding with silence at the beginning would probably solve this.

 

[thothsong]

I haven't even tried measuring with REW, but my preamp sometimes fails to play back the initial chirp. A bit more padding with silence at the beginning would probably solve this.

Do you have the same problem with the original WAV file, or is it only a problem with the Atmos files? The files currently have a 3-second lead, as generated by REW. I don't see an option in REW to generated a longer lead, so I'd have to splice in silence (which is doable).

 

[canavan]

Do you have the same problem with the original WAV file, or is it only a problem with the Atmos files? The files currently have a 3-second lead, as generated by REW. I don't see an option in REW to generated a longer lead, so I'd have to splice in silence (which is doable).

I hadn't realized that I had to switch to audio playback mode to even see the WAV, so I haven't tested that. Playing back the mp4 in video mode is irritating on my Oppo, because the screen turns black.

An 8 second lead in would be better. With sox, that's easy to automate:

sox -n -r 48000 -c 1 silence.wav trim 0.0 5
sox silence.wav in.wav out.wav

 

[thothsong]

An 8 second lead in would be better.

Do you normally have problems missing the beginning sounds for Atmos playback in general? Just trying to understand if this is normal for your playback chain, or if something unusual is causing it. 8 seconds is a relatively long time, but I guess it gives someone time to step out of the room if desired.

 

[canavan]

Do you normally have problems missing the beginning sounds for Atmos playback in general? Just trying to understand if this is normal for your playback chain, or if something unusual is causing it. 8 seconds is a relatively long time, but I guess it gives someone time to step out of the room if desired.

8 seconds is very generous and should be sufficient for (almost?) all AVRs, and that's the value the french dealer suggested that supplied me with the raw files for the Smyth Realiser. I'm not entirely sure how long my processor takes to start playback of a stream, since that appears to depend on whether the previous stream used the same codec or not, but it appears to take between 3 and 5s. I don't really care, since my JVC projector takes much longer to display an image.

 

[thothsong]

8 seconds is very generous

I agree I'm looking at it from the other end, which is, it slows down the measurement process for those who don't need the longer lead.

 

[thothsong]

I'm not entirely sure how long my processor takes to start playback of a stream

Here's a link to a single file with an extra 5 seconds added, see if it's reliable for you:

1M_20_to_20000_48k_L_5s_pad.mp4

drive.google.com

 

[canavan]

Here's a link to a single file with an extra 5 seconds added, see if it's reliable for you:

1M_20_to_20000_48k_L_5s_pad.mp4

drive.google.com

The extra 5s are definitively sufficient that the timing chirp is always audible.

The wav file is pretty weird, neither my Oppo nor flac like it, I've converted it to flac with ffmpeg, and the result always has an audible chirp, even with "only" 3s silence.

 

[thothsong]

The extra 5s are definitively sufficient that the timing chirp is always audible.

The wav file is pretty weird, neither my Oppo nor flac like it

Odd, the WAV file is as-generated by REW.

I'll produce a new set of files with 5s added, perhaps later tonight.

 

[thothsong]

OK, here's a new set of files:

1M_20_to_20000_48k_V3.zip

Atmos 9.1.6 sweeps for REW

drive.google.com