ProDigit
Posts: 374
Joined: Tue Aug 30, 2011 1:24 am

Re: Audio and HDMI?

Wed Jan 04, 2012 8:31 pm

Hi,

Suppose I am playing back a movie from the RPi, but I don't want audio from my TV speakers, but from some studio monitors or home theater, (something very common in many households), can it be done over analog out?

I hate to see there be no analog out when connecting the rp to HDMI

dom
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 5398
Joined: Wed Aug 17, 2011 7:41 pm
Location: Cambridge

Re: Audio and HDMI?

Wed Jan 04, 2012 8:35 pm

There is analogue audio out (headphone socket) that can be fed to an amplifier, but the quality is lower than HDMI audio.

Ideally you would want to use an AV receiver that takes audio from HDMI and feeds it to speakers.

gruetzkopf
Posts: 10
Joined: Wed Jan 04, 2012 7:01 pm

Re: Audio and HDMI?

Wed Jan 04, 2012 8:37 pm

Even if it wont be possible to do that, you should be able to hook up your system to your TV's headphone out.

But what would be really useful to me (althought you can workaround with usb soundcards) would be being able to play two entirely seperate streams via Digital audio and analog out.

tonycollinet
Posts: 38
Joined: Sat Dec 10, 2011 4:12 pm

Re: Audio and HDMI?

Wed Jan 04, 2012 8:57 pm

Or better still the TV line level audio outputs (Normally RCA Connectors). Failing that, audio out from a scart socket.

jaygee
Posts: 18
Joined: Wed Dec 28, 2011 3:18 pm

Re: Audio and HDMI?

Wed Jan 04, 2012 9:43 pm

This set me thinking as I aim to connect the RasPi to a DVI input monitor (with a HDMI to DVI cable) and this will not access the sound on HDMI. My monitor also has 3.5mm jack input or I may use separate speakers but could anyone confirm whether the analogue audio output from the board is mono or stereo? The pcb pics appear to show enough connectivity for stereo but I haven't seen this specified (apologies if it is in the info and I've missed it).

Also, can anyone give any better idea of the audio quality available on the analogue output. Is it just for headphone/monitor use or would it be ok through a decent quality speaker setup?

I would hope that as a mobile phone chip is being used the quality/stereo capability should be at least comparable to music played on a smartphone.

Final thought - is the audio output actually live when HDMI is in use (I gather that it is either/or for the video).

dom
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 5398
Joined: Wed Aug 17, 2011 7:41 pm
Location: Cambridge

Re: Audio and HDMI?

Wed Jan 04, 2012 10:07 pm

The headphone jack is stereo.

Mobile phones would use an external audio codec (e.g. Wolfson), which is very high quality.

Raspberry Pi uses PWM on a GPIO pin with some filtering. It's not so high quality.

If you are playing through speakers built into the monitor, or small powered PC speakers, then it will be fine.

If you have an expensive amplifier/speaker set up, then I'd really recommend using the HDMI audio.

dolafson
Posts: 3
Joined: Wed Jan 04, 2012 10:04 pm

Re: Audio and HDMI?

Wed Jan 04, 2012 10:11 pm

I bought a USB sound card with spdif in/out as well as the standard analogue connections.  It uses the CM106 chipset and works great running Archlinux ARM.  The best part is I bought it off Ebay for under $15 including shipping.

arm2
Posts: 253
Joined: Thu Dec 15, 2011 3:46 pm

Re: Audio and HDMI?

Wed Jan 04, 2012 10:15 pm

Sorry real answers just one more question. I wonder if using Digital Video and analogue sound will be in sync! I'm sure Broadcom will have it right but will external digital units delay the display[1]? Freeview (TV aerial digital TV in the UK) can have sound and vision ridiculously out of sync 0.5 seconds!

[1] I would have thought analogue sound will have zero delay once its left the DAC on the BCM2835 but each piece of digital equipment in a chain always seems to have a delay of at least one frame.

I presume using HDMI sound should! keep things in sync, though I'm not sure how many monitors with HDMI have HDMI sound.

dom
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 5398
Joined: Wed Aug 17, 2011 7:41 pm
Location: Cambridge

Re: Audio and HDMI?

Wed Jan 04, 2012 10:40 pm

Audio sync is a feature of the media player.

But, sure, the openMAX API we use allows an offset to be specified between audio and video to compensate for the delay in, for example, the receiver.

jaygee
Posts: 18
Joined: Wed Dec 28, 2011 3:18 pm

Re: Audio and HDMI?

Wed Jan 04, 2012 10:45 pm

Thanks for your info dom

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