Network Media Players, DACs, Codecs and Optical

keyboarder

keyboarder

Active Member
I'm have 2 original Xboxes running XBMC... then a shared folder on a home PC that is full of music and movies.

(This isn't streaming, all decoding is done on the Xbox, the files are copied through the network from a share on a PC, but that is not streaming. Pandora is streaming. Some setups stream from PC to player, this isn't it.)

CDs sound very good on the Xbox.
FLAC or 320k MP3's, sound only fair on recordings I know are high quality.

This must mean the DAC is different, or there's some other middlemen involved when playing digital files rather than from disc.

That's the XBOX SPECIFIC stuff. Below applies to all others.

If I get an Xbox 360 or ideally a Roku both of which have optical outputs, can you tell me what limitations/strengths the hardware has? I would hope to output a clean, perfect digital signal to my Denon receiver with an optical cable and let the receiver handle all DAC functions at 24bit/96k.

With CD/DVD's that makes sense. I'm sure any receiver knows these formats so I assume the player is just a reader at this point, relaying the binary data from the disc out it's optical port for the DAC on the other side of the cable to convert. Or am I wrong, maybe there is some conversion that happens?

Here's where it gets tricky for me. The media players (which are just small computers) must decode all manner of formats before it they pass them out the optical port in a more generic format, because a dedicated DAC or receiver is not going to know what a flac or ogg or mp3 is. This seems like a source of quality loss on these devices, correct?

My Goal is to play digital media that is equal to or ideally higher quality than a CD's 16bit/44.1k limitation. With my current configuration my media files are substantially worse than CD's right on the same hardware.

Any input?
 
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I started with an original Xbox and XBMC and it sounded worse than CD. I noticed a big improvement when I switched to a PC and a high end sound card. The DAC doesn't know whether it's playing FLAC, OGG or anything else. The computer sends a PCM stream to the DAC. There is one consideration for sound quality: the application must be capable of bit perfect audio (no resampling). In Windows this is done with a playback application and audio hardware that supports ASIO or WASPI drivers.
 
Do you know if a Roku, Xbox 360 or other network media player can produce a bit perfect PCM stream that hasn't been resampled?

Thanks so much for that reply, that gives me some great information to research. If I need to setup a PC I can but it would sure be nice to be able to use something as versatile as the latest Roku.
 
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I found quite a bit of good info about PS3
here

PS3 Audio

The PS3 supports many different audio formats, either disc based, network streaming, or via fixed and removable flash storage like the internal harddrive and external memory cards. In addition, because most of the advanced audio support is done via software on the Cell, the feature list is constantly changing. The following information is based on the latest firmware at the time of this writing. Feel free to come back for updates to the compatibility charts that follows. Also, because of limited analog output options for surround sound (the AV Multi analog cable only has stereo left and right channels), you need to purchase an Audio (and/or Video) Receiver that support "HDMI in" to enjoy 5.1 or 7.1 surround channels. TOSLINK (optical digital) AV Receivers are not recommended because it has a lower bandwidth and it is also an unprotected link, restricting output of high bandwidth and protected audio. Basic HDMI 1.1 that has 7.1 analog outputs for speakers (and a passthrough HDMI for the video to your HDTV) is recommended. Because of the various ways to connect your speakers to the PS3, how you choose the connection determines the quality of the audio output.

Digital versus Analog

The PS3 can do all of the stages above, but depending on the connection, it may skip some of the later stages if you have the right equipment that can handle it. The three main audio output options on the PS3 are the HDMI, TOSLINK (optical digital), and AV Multi cable. HDMI and TOSLINK are digital connections, whereas the AV Multi cable is analog. Both HDMI and TOSLINK can support more than two channels of audio (up to 7.1 for HDMI and 5.1 for TOSLINK), while the AV Multi cable can only support two analog channels (left and right) for connecting directly to the two RCA jacks that lead to your speakers (or amplifier/receiver).

Bitstream versus Linear PCM

The PS3 provides options for either "Bitstream" or "Linear PCM" when outputting the audio signal. This option is located in the "Settings->BD/DVD Settings->BD/DVD Audio Output Format(HDMI)" and "Settings->BD/DVD Settings->BD Audio Output Format (Optical)" settings of your XMB. Linear PCM is audio data that is not encoded (nor compressed) and is in it's pure digital form, ready for conversion into analog for the speakers. A regular CD stores all its songs in Linear PCM form. Most audio starting with the DVD store digital data encoded and compressed (like Dolby Digital or Digital Surround). If "Bitstream" option is selected, the PS3 will take this encoded and compressed audio and send it untouched to the HDMI or TOSLINK cable for your external decoder to decode. In other words, the receiver at the other end of the HDMI or TOSLINK must have special chips that can decode and uncompress formats like Dolby Digital and DTS Digital Surround, and then convert the resultant Linear PCM to analog (via a DAC) for the speakers connected to the external decoder. If "Linear PCM" option is selected, the PS3 will actually decode the audio into Linear PCM first, before sending it to the HDMI or TOSLINK. In this case the receiver on the other end of the HDMI or TOSLINK only needs to convert the Linear PCM to analog for the speakers connected to it. Because of the current bandwidth limitations of TOSLINK, choosing Linear PCM (the decoded and uncompressed signal) on this connection limits you to only two channels of audio. For multichannel (like 5.1) over TOSLINK, you must use "bitstream", which uses smaller bandwidth of compressed and encoded data.

Audio Storage Formats

As disc based storage medium became popular it was feasible to store audio digitally. The first digital format was basically the CD (red book), which stored 44.1kHz of Linear PCM (plain uncompressed and unencoded 16bit digital). In order to store multiple channels (up to 7.1) efficiently, many formats that took advantage of compression and encoding were invented. The DVD introduced 48kHz sample rate, and many types of encoding. The following table describes the various audio formats (those in pink are not supported by PS3).
 
Only certain models of the ps3 had SACD support- see bottom of wiki page for breakdown:
http://en.wikipedia.org/wiki/PlayStation_3

The current model in production doesn't have SACD support - looks like only the earlier models had it. Lucky for you, that means that you can pick up a used one for a nicer price, if you are inclined ;)
 
It's starting to sound like I'm going to need a complete set top PC to get full sound quality from my FLAC and 320k MP3 digital files.
 
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