Hi-Rex LPCM over HDMI

Could I passthrough 192/24 (full hi-res) LPCM over HDMI to my AV controller using applications like Onkyo HF Player, Hibiki and FLAC player? Would Apple TV downsample everything before the output?

With regard to PCM/LPCM, the new TV supports both AIFF and WAV files as do older models. Not sure about 24-bit sampling as I normally use 16-bit/48.0K sampling when recording and just leave the TV audio setting in the "Auto" mode. (I.e., I assume the current audio switch "Auto" setting passes source data "as is" while the "16-bt" setting forces re-sampling up or down to 16-bit for hardware compatibility if needed and assume the new model will have similar settings.)

Added: Just tested a 24-bit, 44.1 KHz AIFF file with a data rate on the order of 2.1 Mbps. The file sounded the same to me on my computer's Logitech external amp/speakers as it did through an TV3 on my Pioneer/Bose home entertainment system—but then I don't claim to have pitch perfect hearing either. I assume the TV4 should have the same capabilities.

FOLLOW-UP:

Finally managed to locate and download some 24-bit/192.0 KHz WAV sample files and perform preliminary tests on them. iTunes was able to manage the content at its original resolution and stream it thru an TV 3 unit to my home entertainment system where it played back as PCM. Unfortunately, I have no way to scope or otherwise determine data specs as played back by the receiver since these levels of quality are beyond my ability to quantify the results aurally but can qualify them as sounding great. It is assumed this WAV workflow would be carried over to the TV 4 but you would have to measure the final resulting quality yourself.

informedandarrogant wrote:

Hi all,

I am interested in buying the new Apple TV (4G). Since it only has an HDMI sound out (curse DRM) I was wondering what its limitations are.

I am an audiophile and have a growing library of DSD, 96/24 and 192/24 recordings that I would like to play with nominal resolution through the Apple TV, directly to my Receiver/DAC.

Could I passthrough 192/24 (full hi-res) LPCM over HDMI to my AV controller using applications like Onkyo HF Player, Hibiki and FLAC player? Would Apple TV downsample everything before the output?

You'll have to wait until it's actually available (tomorrow hopefully) to find out, but to be honest I doubt it.

AppleTV1 maxed out with 44.1 kHz 16 bit LPCM for audio

AppleTV 2/3 resample everything to 48 kHz/16 bit.

Let's hope ATV 4 does better but until Apple sees HD audio as important to the consumer masses I doubt anyone has even considered HD audio support.

One of the issues with AppleTV is that in the past it's been a 'hobby' and now it'll be a vehicle for AppStore sales of mostly dross.

It has never sadly been imbued with any audiophile or videophile features.

AppleTV 2/3 resample everything to 48 kHz/16 bit.

Not an audiophile (or technician) that the OP (or you) is (are) but do like to know how things work, as well as, their limitations. Was wondering if you could amplify the above statement. Have you determined if the downsampling occurs in the serving software, the TV device itself, or if it is a by-product of the HDMI interface level being used? Also, if a by-product of the HDMI interface level, do you know the limitations for the latest 2.0 and above levels? Lastly, are you saying that the resampling software switch currently used in the TV firmware is monotonic in nature—i.e., only forces up-sampling of audio <16-bit?

Am personally more interested in possible future 2K/UHD/4K capabilities to go along with the latest TV 7.1 surround sound audio feature and what is actually being sent to/received by my audio system when playing blu-ray/HFPA optical discs using the various "pure/true/uncompressed/master" audio formats via current HDMI 1.4 cables. Unfortunately, the only way I can examine HDMI output is to "capture" it using hardware encoders having sampling limitations lower than the source content being tested.

Therefore, would appreciate any additional information you can provide and believe the OP, as well as, other readers might also appreciate such insights. (I.e., IMHO this is a very interesting topic for discussion.)

OK, I am playing an Apple Lossless ripped at file 24bit/96khz/2918kbps.

When I first played the track, direct from iTunes using the ATV4 as a "speaker" it appeared as a 5.1 track! There is a known bug in the ATV4 tvOS 9.0 which means you have to force Dolby surround for movies in the audio settings, else they play in stereo. With this setting, when I first played the track, the ATV continued to force Dolby 5.1: 48khz, 640kbps. I haven't been able to replicate that since, but another little bug there somewhere.

When forcing surround was turned off, my lossless file was sent as 2ch PCM, 48khz. No bitrate info available. The same appears whether the track is played via iTunes or via the ATV4 interface. In either case there is downsampling to 48khz.

Server: iTunes 12.3.0.44

Connection: gigabit ethernet

Receiver: Yamaha RX-V3067

Hope that is helpful.

Jon Walker - it won't be a limitation of the HDMI profile used. The very first HDMI 1.0 standard included support for 192kHz/24bit 8 channel PCM to be carried. Later spec revisions added support for newer, lossless compression like Dolby True HD and DTS HD Master Audio to be bitstreamed (rather than decoded to PCM)

Of course not all HDMI sources will support >16 bit audio or >48kHz sampling rates - but the standard itself has done since the beginning.

Jon Walker - it won't be a limitation of the HDMI profile used. The very first HDMI 1.0 standard included support for 192kHz/24bit 8 channel PCM to be carried. Later spec revisions added support for newer, lossless compression like Dolby True HD and DTS HD Master Audio to be bitstreamed (rather than decoded to PCM)

Of course not all HDMI sources will support >16 bit audio or >48kHz sampling rates - but the standard itself has done since the beginning.

Steve—Thanks for the PCM background information.

Only thing new I've noted in reviewing old Mono and Stereo DD files is that they appear to be "passed through" in the "Dolby Surround" mode as opposed to being "forced" to AC3 as are AAC, MP3, Apple Lossless, M4A, etc. Implies there is still hope that LPCM recognized audio may also be passed through in the "Auto" and "Stereo" modes but then brings up the question regarding possible built-in differences between 7.1 and Stereo sampling standards.