Does Sound Check work over Airplay from iTunes?

[hineni]

I swear it used to, but at some point Sound Check stopped working over Airplay. I’m playing from my iTunes library to some Airport Express units. Neither the analog nor digital outputs of the AE are volume-normalized. I can get it to work by setting iTunes output to Computer, then Computer output to an Airplay device, bit that’s a huge hassle.  Any ideas? 

[kirkmc]

I don't see why AirPlay should have any effect on Sound Check. I don't use it currently, but have in the past; I stream from my iMac to a Sonos Amp in my home office. If it's not working, then that's clearly a bug. 

[hineni]

I can verify that Sound Check indeed does not work over Airplay. Maybe it’s a bug, or maybe it’s Apple’s disregard for local playback and streaming, but it just doesn’t work. 
 

I just discovered a workaround, using Rogue Amoeba’s Airfoil to snatch the audio before it gets to the speakers (after Sound Check) and stream that to an Airplay receiver. 

[kirkmc]

How do you verify this? Do you have music where it's obvious when Sound Check kicks in? 

[hineni]

Kirk, Í chose a track with very low volume (a Brian Eno ambient track) and one with a very high volume (from Traveling Wilburys Vol 3) and compared with headphones directly to the analog jack on my iMac (Sound Check works) and via Airplay to an Airport Express and optical or analog out to a headphone amp (no Sound Check). BTW, I’m on an iMac running Mojave. 
 

And want to say, Kirk, I’ve been enjoying you work for years. Glad you’re here!

[kirkmc]

I tried, and, yes, it isn't apply Sound Check corrections. Playing a soft and loud track isn't necessary. If you select a track and press Command-I, then look at the File tab, you'll see the Sound Check correction in dB. So what I did was play a few tracks with Sound Check off, and I recorded them with Audio Hijack. I then played the same tracks with Sound Check on, and recorded them, and simply looked at the waveforms to see the difference.

 

So Airfoil is one option, and you might also want to check out Rogue Amoeba's Loopback, which should also allow you to do that. (I haven't tried it.) 

 

Since I never use Sound Check - it sometimes results in noticeable artifacts - I'd never noticed this before. 

[hineni]

For those interested, the Audio Hijack program used with Airfoil as an Airplay transmitter does get Sound Check working over Airplay. If anything, Airfoil seems more stable than Apple’s native Airplay, with quicker speaker selection and fewer dropouts. 
 

It’s puzzling that Sound Check no longer works over Airplay; I think it stopped working around the time Airplay 2 rolled out. I do most of my listening over Airplay/Airfoil, with lots of random play of genres and playlists, so I’m glad to have this sorted out.