[This article covers using a Mac's HDMI output for surround sound audio using an HDMI equipped A/V receiver. Info here may not be applicable to later macOS versions and newer Macs, as macOS Big Sur DVD Player app has no Disc Setup preference settings. Also here's a article with Notes/Tips for Repeated Mac Mini Video Blackouts with some A/V Receivers that includes Receiver HDMI Info, Tests and Tips on HDMI and HDCP problems in OS X.]
(from a reader question)
"OS X DVD Player HDMI Audio Question
I finally hooked up my new mac mini to our receiver so we'd have surround sound possible with DVDs played in OS X. The OS X Sound pref pane set to HDMI Output (see example below) and Audio/Midi utility configured correctly for multi-channel audio. (I think.) The receiver the mini's HDMI is connected to shows "PCM" during playback and DVD movie (Dolby Digital 5.1) audio seems muffled compared to playing the same DVD in our home dvd player. We noticed the standalone player shows "Dolby Digital" on the receiver's display - not "PCM". DVDs just sound much better from the home player than from the OS X DVD player connected to the same receiver.
How do I get the OS X DVD player to send 'dolby digital' to the receiver to see if that helps?
First, I'm assuming your OS X Sound Output (System prefs) is set to HDMI like this example:
OS X Sound Output Preferences
(The TV Name is listed even when HDMI connected to AV Receiver)
FYI: When set to HDMI audio output, the Mac's audio volume control is disabled.
Volume is controlled from the connected device (i.e. Receiver or HDTV).
As for changing the OS X DVD Player audio output to Dolby Digital (and not PCM) - it's a simple change in the OS X DVD Player settings. Set the OS X DVD player Prefs (in 'Disc Setup' options) Audio Output to "Digital Out". (FYI: macOS Big Sur's DVD Player does not have the Disc Setup preference options shown in the screen from an earlier OS X DVD Player below.) As you had it set (from the comments above), the OS X DVD Player was decoding the Dolby Digital audio on the DVD and sending PCM audio to your receiver. (When set to Digital Out, it will bitstream Dolby Digital (or DTS) to the receiver for decoding.) Apple's support article on "Setting up iTunes & DVD Player for digital surround sound" (support.apple.com/kb/HT4072, later changed to HT202029), went from "archived, no longer updated" to removed as of 2019. Here's a screenshot from my OS X DVD Player Audio Output prefs setting.
OS X DVD Player "Disc Setup" Preferences
The "Digital Output" option may also have info on the connected device appended to it. (My example above has "Samsung" - the TV brand connected to the AVR. If not going through a receiver, you'd usually get only Stereo with direct TV connections.) As you can see in the screenshot, I also check the option to "Disable Dolby dynamic range compression". (I prefer maximum dynamic range although some may not, especially for nighttime viewing. A/V Receivers often have DRC options also.)
iTunes Surround Sound Settings:
The Apple article also had info on surround sound setting in iTunes. Click the "Speech Bubble" icon (see below) to see/select available audio options for the specific file being played. Apple says in iTunes 11 and later, digital surround sound is selected automatically for content that includes it. (Surround output still relies on proper hardware/configuration and options can vary depending on the media used.)
I rarely use it and don't buy/rent iTunes content so can't comment on quality or specific recommended titles.
OS X DVD Player (Subjective) Sound Quality (PCM vs Bitstreaming/Digital output)
After Beth's comments on (PCM) DVD movie SQ, I checked this on my AVR (with TDKR DVD's Dolby Digital 5.1) and PCM output from the OS X DVD player seemed (by ear) about 5-6dB down vs Bitstreaming at the same AVR Master Volume setting. Lower volume (level) with LPCM vs Bitstream isn't uncommon, but even adjusting for volume level, I still preferred bitstreaming Dolby Digital/DTS to the AVR as it also shows the codec used on the AVR display (vs 'PCM'). Often in blind speaker tests most think 'louder' is better, within limits of course. Normally from a standalone player, SQ should be equivalent (PCM vs Bitstream) unless there's another issue present. (I used a 2012 Mac Mini 2.3GHz quad-core i7, 16GB RAM with OS X 10.9.5. Not tested other versions/player software.) Bottom line, I prefer letting the A/V Receiver decode DVD surround sound rather than OS X. (And one less thing the Mac/OS X has to do.)
And in case anyone is wondering, I was getting multi-channel PCM out. (Audio/Midi utility set for 8-channel (7.1) output. Notice this is NOT set to "Encoded Digital Audio" option. I prefer PCM out for general (non-DVD, non-iTunes movie) playback through the AVR. Digital/Surround is set separately in the DVD Player and iTunes.) The OS X 5.1/7.1 speaker tests in Audio/Midi Setup Utility worked/played correctly (front, center, rears, subwoofer, etc. output tests) and the (Yamaha RX-A2000) AVR (set to straight surround decode/no DSP) speaker icons display showed 5.1 or 7.1 depending on my configuration set in Audio/Midi utility.
OS X Audio/Midi Setup Utility Settings
(Clicking each Speaker will send a test tone to it)
(I originally linked to Apple's PH5164 article on "Using Audio Midi to Setup external speakers for stereo or surround sound", but they have now removed it. And their basic guide to "Connecting a Mac to a home stereo, iPod, iPad, musical instruments, or speakers" was revised to "Set up an audio device on your Mac or stream music from your Mac", but as of 2021, HT201739 is no longer online.)
BTW: I tried 5.1 vs 7.1 PCM tests with DVD Dolby Digital 5.1 in case using Dolby Digital 5.1 with 7.1 setting was a factor - it wasn't. Maybe other models/OS versions or players differ, but I see no reason not to set the DVD player to Digital Out unless your connected hardware/setup has an issue with that.
I also like that Bitstreaming shows the DVD/Movie's Codec used on the AVR's display instead of just "PCM". (Although I've not had the problem with my setup, as mentioned on the Audio/Home Theater page previously, some have had to set their player to PCM to avoid audio dropouts with some Dolby TrueHD audio Blu-Rays when the player was set to bitstreaming. The only time I've set my BD player to PCM is to hear director's commentary/secondary audio tracks/PIP - something I rarely do.)
About Subwoofer (Low Frequency Bass and .1) Output:
I've seen some posts in Apple's forums from mac owners saying they're not getting any subwoofer output from their Mac/OS X systems. I didn't see any detailed info on their configuration/setup but here's a list/recap of some tips, reasons why and things to check:
- Does the content being played have any actual low-frequency content?
- How is your A/V Receiver setup for Bass/Subwoofer management?
(Are speakers set to "Small" with subwoofer crossover frequency set (i.e. 80Hz), etc.)
- Does the Subwoofer work correctly with other content? (non-OS X player, DVD/BR discs, etc)
- Does the Subwoofer have an auto/on switch? (if so set to ON vs auto - more info below)
- Does the A/V Receiver have an option for 'expanded' surround options (but you may not like it)
Some AVRs also have a "double bass" (or similar named) option for sending main speaker channel (not .1) low frequency audio to the Subwoofer(s) even when speakers are set to "Large". That usually isn't recommended however and setting speakers to "Small" (regardless of their size/driver capability) is preferred as it reduces the amplifier load significantly by not having to handle LF (low frequency bass) output, and lets the Subwoofer do what it's designed to do better than the main speakers. This load reduction is a plus for most Receivers and can help extend the life of the amp and improve audio dynamics. (Low Frequency audio takes a LOT more power.)
Regarding Subwoofers with an Auto/On Switch:
Some subwoofer amplifiers with an "Auto On" (or Auto Standby) feature may not be getting a high enough level signal to turn on the amp. This can vary by subwoofer/amp mfr and also by AVR. (Some AVRs output higher voltage levels than others. Regardless I don't recommend setting the AVR's SW trim level over the '0" setting as it could clip the output in some cases and reduces headroom.) Another old tip (for higher levels/better Auto on triggering) is using a "Y" adapter at the Subwoofer if its amp has dual (R/L) inputs, but this could also clip the input stage of the SW Amp, depending on the AVR/Output level. Some higher end SW amps handle this better (input protection) but many may not.
Also some subwoofer amps with an "Auto" on setting may go into standby if no (sufficient) signal is received for a period of time. (The SW plate amps I've had with this feature typically went into standby after appx 15 minutes. Despite them being fairly quick to switch out of standby, for some movies with extended periods of dialog, I've switched them to On vs Auto for that reason.) Despite the auto/standby feature, I still power off my amps when done using them.
(There's a lot more to this subject of course (room calibration/EQ, gain vs level matching subs, etc), but it's beyond the scope of this article.)
The Yamaha AVR has dual subwoofer outputs and unlike some ".2" AVRs, the outputs are separate/independent. (You can setup Subs for Mono x2, Stereo, or Front/Rear configuration, although in most cases Mono is best.)