Audio Configuration Guide - Plex Home Theater

Warning!: Plex Home Theater is deprecated and no longer in development. We have focused our efforts on the newer Plex Media Player app instead and recommend moving to that app.

Basics

Digital audio can be a bit of a mess and there are most certainly better places to get a primer on it than this article, so the text here should just be considered a quick overview. What you need to know is that there are two major ways to handle audio in the digital age, PCM (or direct or LPCM) and passthrough (or encoded).

PCM/Direct means that the audio decoding is done in software (i.e. Plex Home Theater does it) and then sent to the receiver that "just" outputs the PCM streams (one stream per channel) to the speakers. Traditionally you can only pass two channels via PCM, but LPCM (linear-PCM) allows for up to 8 channels.

Encoded/Passthrough is what it sounds like: PHT just takes the encoded stream and passes it to the receiver which does the conversion from encoded formats to PCM and then outputs it. In theory, this might sound better since the receiver is probably better at doing that conversion, but the audio quality difference is not something most of us can actually hear.

One important difference is where downmixing is done. For example, if you have 2 speakers connected to your receiver and you have source media with 5.1 channels (or 5 speakers and material in 7.1), the audio needs to be downmixed to hear all the sounds. When you are outputting in PCM mode the downmixing happens in PHT; if you are running pass-through the downmixing will happen in the receiver. This is also true about volume amplification: that will only work if the decoding is done in PHT, otherwise volume must be controlled by your receiver.

Formats

There is no single digital format for audio, there are many. The most common are:

  • MP3: Only carries 2 channels and is relatively low bitrate. Not that common for new releases.
  • AAC: The closest thing we can get to a universal standard these days. The drawback with AAC is that while it can carry 6 channel sound, not many receivers handle it and it's not designed for it. (It's telling that Apple—the champion of AAC—doesn't even support AAC as a raw format in their products.)
  • Dolby Digital / AC3: The most common multi-channel format. It handles at most 6 channels (5.1) and is supported natively by almost anything. However, it's relatively low bitrate so it might not give the best fidelity. Most TV shows have AC3 tracks.
  • DTS: Most common for movies, handles 6 channels at most, and is pretty universally supported in mid-range equipment and up. Low end equipment usually does not support DTS natively since there are licensing fees involved. The AppleTV, for example, supports AC3 but not DTS.
  • TrueHD: TrueHD is Dobly's successor to AC3. This codec is lossless and supports 8 channels. High end equipment is needed to get native TrueHD support.
  • DTS-MA: The successor to DTS. It is backwards compatible with DTS. DTS-MA is lossless and supports 8 channels.
  • Others that you can run into but are not common: Vorbis, FLAC. Both supports multiple channels, but few receivers natively support them, even though at least FLAC is on the rise.

Setting Plex Home Theater Preferences

Determine your connection options.

When you start PHT for the first time it will ask you for the type of connection you have. You can select Analog, Optical, or HDMI:

  • Analog: You connect something to the headphone jack or using built-in speakers on your laptop/computer. This configuration is very simple and standard analog will not handle any multi-channel audio.
  • Optical: These connections most commonly use a S/PDIF connector. This is built-in to all Macs and most other modern motherboards have it as well. The S/PDIF protocol can play 5.1 with two data formats: AC3 (Dolby Digital) or DTS.
  • HDMI: This handles both video and Audio and is the best choice if you want to have full codec support. HDMI has the most available bandwidth in its current form and handles all formats natively (AC3, DTS, TrueHD, DTS-MA, LPCM).

Additional Audio Settings

You'll configure your audio settings under Preferences > System > Audio Output in PHT.

Receiver Support for Formats

If you are using a digital connection (Optical or HDMI) you need to set whether or not your receiver supports AC3, DTS, or LPCM. You can refer to your receiver/TV manual to find out what formats it supports (see explanation of formats above). Select the appropriate choices here.

If you mistakenly enable something you shouldn't, you will get stuttering when PHT tries to send something unsupported to the receiver. If you are unsure, leave them all unchecked and you can try to enable them one at the time to see what works.

Boost Volume Level on Downmix

When downmixing from 5.1 to less channels, PHT will try to increase the volume of the speech track to make it more audible. If you hear distortion you might want to disable this.

Audio Output Channels

This option leads to a lot of misconceptions. This option is only used when not using passthrough. For example, when you have DTS unchecked but LPCM enabled it will transcode DTS audio to the number of channels configured here. Configure this option to match up with the number of speakers you have, but don't expect it to be used if you only play encoded audio.

Audio Output Device

The actual device used when not playing encoded or passthrough audio. Sound effects and analog audio is output from this device. On Windows you will have two entries for each device, one DirectSound and one WSAPI; these are two different Windows APIs. DirectSound is an older, more compatible API but will not work with new HD audio formats (DTS-MA/TrueHD) while WSAPI is the new nice API, but might cause issues for some users. For analog audio you should select the DirectSound device if it works (otherwise just switch to WSAPI and test that).

Passthrough Output Device

The audio device that should be used when playing passthrough/encoded audio. On Windows, if you want to enable DTS-MA/TrueHD formats you need to use WSAPI devices here.

Troubleshooting:

Still having problems? No audio? Stuttering? Start your testing by unchecking all passthrough formats. If things work, enable options one at a time until you determine which causes problems. On Windows you might want to try to switch between DirectSound and WSAPI on both output devices to see if it makes any difference.

Tip!: If you're not hearing any sort of sound at all regardless of settings, try hitting the + key during playback. It may be that the volume is somehow set too low.

Still having problems after that? Make sure to screenshot your configuration, collect a debug log file, and create a new thread in the forums.

Related Page: Plex Apps > Reporting issues with Plex Home Theater
Related Page: Plex Home Theater Forum

More information:

Related Page: XBMC Wiki - How To: Configure Audio (can be helpful with more advanced details)
Related Page: XBMC Wiki - Windows Settings for AudioEngine