XAPBob
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Re: Audio options...

Tue Jan 03, 2012 3:37 pm

According to this thread: http://www.raspberrypi.org/for.....udio-input there is no audio input.

Is this a limitation of the chip, or of the connections?

I'm thinking about the ability to use a raspberry as a cheap audio streamer, which could be co-located with an FM transmitter for a charity radio station I help with each year.

This means I'd not need the output...

Of course if it is a chip limitation (which is understandable) then can I vote for a possible extension at some point  until then I'll have to run an external sound card...

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abishur
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Re: Audio options...

Tue Jan 03, 2012 3:46 pm

This is just my educated guess, but knowing that the chip used is very similar to what we carry around in our pockets most days (cell phones ) and also knowing that this same chip is used in the Roku 2, then my guess is that it is a chip limitation that prevents audio input.  I would further venture that *somewhere* there's a mic input, but assuming such an input actually existed, I would imagine that it is a low quality mono input and not a high def (or even CD quality) stereo input.

But hey, that's just my guess
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Chromatix
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Re: Audio options...

Tue Jan 03, 2012 3:49 pm

There are plenty of USB soundcards for your audio input needs.  Many webcams also have a built-in microphone which appears as a separate USB function on the device.
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gimliflea
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Re: Audio options...

Tue Jan 03, 2012 4:51 pm

I have a thought that HDMI can include an audio in stream. Would this be possible on R-Pi. Maybe someone could confirm deny?

jamesh
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Re: Audio options...

Tue Jan 03, 2012 5:14 pm

No HDMI in on the Raspi.

However, I believe there is audio in on the SoC - required for video recording. Not sure of the quality though, and I don't think its connected on the Raspi.
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error404
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Re: Audio options...

Tue Jan 03, 2012 6:43 pm

Apparently the SPI peripheral also supports I²S, which most/all CODEC chips support for digital audio data. SPI is apparently broken out on the board, so assuming (big assumption...) that a driver/documentation for this peripheral is provided that supports using it in this mode, you could just add any audio ADC/CODEC of your choice on a breakout board.

USB audio is sure to work though, and even if documentation/drivers are provided, still going to be much less work. But some people like to do it the hard way for fun .

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Gert van Loo
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Re: Audio options...

Tue Jan 03, 2012 10:10 pm

There is no ANALOGUE audio input.

It has PCM and I2S. I have been thinking of making a follow up of the Gertboard which has only two devices: Real time Clock and Audio codec.

Neil
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Re: Audio options...

Tue Jan 03, 2012 10:56 pm

If the Gertboard used a stackable connector for the GPIO then you could have both GPIO and RTC/Audio boards, with perhaps some DIP switches or links to select GPIO taps.

XAPBob
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Re: Audio options...

Wed Jan 04, 2012 8:53 am

Lots of informative replies - thanks all.

Realistically it'll have to be a USB card.  Not a significant problem - linux supported cards seem to be available from £2 nowadays (cheaper than last time I looked).

To add an external dedicated DAC would be rather more expensive (and that somehow goes against the spirit of the thing.

Of course if someone designed a (halfway decent) DAC connector board then that would be a different thing altogether - but it's beyond my current skillset, and way beyond my available time

Xevo
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Re: Audio options...

Sun Jan 08, 2012 11:13 am

Gert said:


There is no ANALOGUE audio input.

It has PCM and I2S. I have been thinking of making a follow up of the Gertboard which has only two devices: Real time Clock and Audio codec.


Which pins would have to be used for I2S and PCM?

If you're going to make a board with an audio codec I would love to see a S/PDIF Out on that one. That way I could use the raspi to feed stereo sound to my amplifier, which has decent DACs. Replacing my PC with the raspi for music playback would be awesome.

I have been thinking about doing an S/PDIF Out myself, because essentially I would "only" need something like the TI DIT4192 (http://www.ti.com/product/dit4192). But I would have problems acquiring a pcb for the chip and the (Cinch/TOSLINK-)Connector, let alone soldering the chip itself on the pcb and somehow getting the OS aware of that output device. And frankly, there are no How-Tos for that kind of thing.

So if you're actually doing a sound-addon-board, please consider S/PDIF.

Efcis
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Re: Audio options...

Sun Jan 08, 2012 1:14 pm

Hi Gert et al.

Gert said :

I have been thinking of making a follow up of the Gertboard which has only two devices: Real time Clock and Audio codec.

For the CODEC, please consider using a device with a large sampling rate capability (eg. TLV320AIC3104 - or even better - TLV320AIC3204). The RaspberryPi and such an add-on card would make a perfect candidate for ham radio hobbyists involved in SDR (Software Defined Radios).

Neil
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Re: Audio options...

Sun Jan 08, 2012 3:25 pm

More likely to be a Wolfson as we have drivers for those already.

ujamer
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Re: Audio options...

Mon Jan 09, 2012 9:37 am

Audio Codec would be an awesome addition! Wolfson does seem like a good idea because of the framework provided by ASoC/ALSA. Broadcom chipsets does not seem to be supported at the moment though.

error404
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Re: Audio options...

Mon Jan 09, 2012 9:49 pm

Really all that's needed is a driver/spec for the I2S interface. Generally the configuration part is pretty trivial I2C or even just a few pins to be pulled up/down on the CODEC.

This is something I'm interested in (particularly for SDR), and I have some experience with audio, so I'd be willing to work on hardware. Not going to waste my time before docs/drivers appear though.

dave3641
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Re: Audio options...

Mon Jan 09, 2012 11:35 pm

Will it be possible to output S/PDIF audio out of the composite RCA connector with custom drivers? Or will it only be possible through a usb or gpio adapter?
I know some mini-itx boards had a jumper setting to swap the rca between composite and spdif but don"t know if this was just a switch or a separate circuit.

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