[mythtv-users] Bit-perfect audio over HDMI

[Jean-Yves Avenard]

Hi

On 27 August 2010 06:38, Dave Badia <dbadia at gmail.com> wrote:
> Hi, I'm currently using an optical connection for my audio between
> mythtv and my receiver and have bit-perfect audio for mythmusic.  In
> preparation for myth supporting blue ray and the lossless audio codecs
> which will accompany them (Dolby TrueHD and DTS-HD which require HDMI
> of course), I've begun experimenting with outputting both video and
> audio over HDMI from my nvidia GT220 card.  Of course, I'd like to
> maintain my current state of bit-perfect audio when playing music.
> Does anyone have this working over HDMI?  Given that only certain
> sound cards support the 44.1k sampling rate, do video cards have the
> same issue?
>
> I ask (as opposed to trial & error) because currently the only HDMI
> device I have is my TV which of course won't accept 44.1k as audio
> input.  I hope to upgrade my receiver within the next few months
> though.
>
> In case it's relevant or anyone is interested, here's the
> configuration I currently use for bit-perfect audio using the digital
> optical output from my Turtle Beach soundcard.  I've overridden the
> audio device in the myth music setting to use ALSA:hw:0,2 to avoid any
> conversions from taking place (note this is hw and not plughw, as
> plughw will resample).  In General settings under Advanced Audio
> Configuration I overrode SRC quality and set it to disabled.  I also
> disabled internal volume controls on the next screen.  Not sure those
> last 2 steps are absolutely required, but I figured best to start with
> everything off and see if my content plays... which it does.
>

Setting SRC to disable in myth doesn't guarantee that you will get
bit-perfect. It just means that myth won't do the resampling itself,
and instead let ALSA handle it.

If your audio card says it doesn't support 44.1kHz, then it will be
resampled by ALSA to whatever the audio card support (likely to be
48kHz).

If your audio card supports 44.1kHz, then that's what mythtv will
output (which is what you call bit-perfect). There's no need to take
the complicated steps you've taken. Myth will always do what's best.

JY