Raspberry Pi gets its own sound card | Hacker News Reader

Raspberry Pi gets its own sound card

engadget.com

48 pointsneya32 comments

I love the fact that a whole ecosystem has appeared around patching up the holes in the Pi's architecture[1]. Unfortunately by the time you've purchased them all, you probably could have bought a BeagleBoard instead.

[1] The built in codec and filtering is absolutely horrible making it pretty useless for audio applications.

I have a beaglebone black, but I can't get it to encode FullHD video in realtime. Am I missing something? or is there actually a justification for both the RasPi and the BeagleBone?

The raspi has a hardware video decoder for some codecs (e.g. H.264) whereas the bbb doesn't. Hence the bbb is not very practical for htpc setup.

usually when people do [1] or something like that it's to a link. to my ear the audio out of the pi's hdmi port is perfectly fine. i think the DAC used in the RCA jack is probably not very good. I would pay for a HDMI audio to DAC adapter rather than $33 for another soundcard that just works with the pi.

Are there any sub-$100 HDMI DACs that do 5.1 or 7.1? That would be amazingly useful if so.

yes, check ebay http://www.ebay.com/itm/AC3-HDMI-Dolby-HDCD-5-1-2-1-96KHz-24...

almost every HDMI decoder chip has 4x I2S outputs and just spits out digital audio

for example ADV7604

Cheap chinese HDMI-2-VGA adapters use chinese made hdmi receivers, those lack proper i2s outputs and provide only 2 channel SPDIF. example: http://www.taker.im/up/138624609420664378890.jpg http://lontiumsemi.com/English/ProductShow.asp?ProductId=4

usually when people do [1] or something like that it's to a link

Offtopic, but footnotes predate the web by quite some time. If only we had a easy way of formatting super/subscript...

No need for formatting; you can easily get superscripts and subscripts in plain text. See Unicode’s Superscripts and Subscripts Block¹.

――――――

¹ — https://en.wikipedia.org/wiki/Unicode_subscripts_and_supersc...

Audio via HDMI is digital so there really are no problems there. The 3.5mm audio jack is just a simple PWM (see plots at http://www.crazy-audio.com/2013/11/quality-of-the-raspberry-...). Sound quality is actually quite improved upon the first release, but it's never going to be great.

If you using it for HTPC then beagleboard is useless as it has no hardware based video decoding. That is why the Pi is so popular for HTPC's, built in H264 decoding hardware

The Beagleboard's probably a bad example in this case, but I've got a Cubieboard with hardware video decode and line-in/line-out that cost me less than the Pi + this board. (I believe it also has SPDIF on one of the pin headers. All of this was essentially free - the SoC it uses has built-in audio DAC/ADC, Ethernet controller, SATA, and a bunch of other neat stuff.) Plus a lot of early Pi purchasers won't be able to use this without buying another Pi, since the original version doesn't expose the I2S interface required by this.

Link: http://uk.farnell.com/wolfson-microelectronics/wolfson-audio...

It's disappointing that this doesn't support v1.0 boards. I hadn't realised that RPis had been fragmented like that.

It looks like the P5 header that it uses was only added in rev2, and "intended to be a suitable attachment point for ... audio codec boards"[1].

It's definitely a shame that things are fragmented, I was considering adding audio to my old Pi. But at least they're cheap enough to justify buying a second one :-)

[1] http://www.raspberrypi.org/archives/1929

Raspberry Pi has USB right? So why not just get a Schiit Modi? A very high quality DAC that can be entirely USB powered.

The USB on the Pi has some issues. A lot of devices need to use an external, powered USB hub because the board can't supply enough. Your ethernet is also going through the USB hub.

The issue with usb on rpi is that it's unstable. It can drop messages. For ethernet it doesn't mean much, because packets will be retransmitted, but for audio it means sound will occasionally stop for a moment. It's very annoing.

The Schiit Modi is double the cost of the Wolfson card and has no audio input capabilities. Seems like for uses outside of an HTPC the Wolfson card provides a lot more flexibility.

What bus is used to communicate with the sound card? The obvious candidate is USB, but the Pi's USB bandwidth is limited and I don't recall whether USB is available on the pin headers.

If it uses the P5 header, then it's I2C - so there are no USB issues. I remember reading about (other?) Wolfson DACs on Raspi and they were using I2C.

It's actually I2S primarily. I2C would be used for control (volume etc I suppose)

there is no USB on the pin headers, unfortunately (Schematic: http://www.raspberrypi.org/wp-content/uploads/2012/10/Raspbe...)

Nice. PI's built in audio processing is extremely crappy and the analog 3.5mm output is almost unusable for music.

How can I actually hear this? I am no audiophile, but I can't notice any audio problems with my Pi.

apparently the DAC for the RCA out is 11bit - but I can't really find any definitive proof of that.

That should be pretty easy to demonstrate by feeding the output back into a decent 16-bit soundcard - the noise floor should reveal any dithering going on (and if there's no dithering it will be painfully obvious that there's only 2048 discrete output values...)

I might have a go tonight.

http://www.raspberrypi.org/phpBB3/viewtopic.php?p=103330 Might be of interest to you.

RCA? Isn't the RCA output for video only? I was referring to 3.5mm green audio output.

right you are - that's what I meant.

I find quality in-ear headphones extremely revealing of poor quality output. Shure e5c, to pick an older set that I own, are especially unforgiving of noisy output stages and cross-coupled interference. The additional acoustic isolation really helps your brain focus on the audio by cutting out the masking effects of environmental noise. This isn't always a good thing.

For example, the Cowon S9 audio player was supposedly designed for high output quality, with a pile of DSP presets for EQ etc. With the e5c's you can really hear the poor quality processing of the EQ, especially on reverb tails. Have to turn the EQ off completely to eliminate them.

By EQ you are referring to equalizer? So if I don't use EQ on RPi (which I don't), I'm good? Is there some particular audio clip which I can sense the crappiness when listening to?

I was talking about a specific hardware player, but in general any additional signal processing has the potential to add artefacts.

To hear these sorts of things, listen for reverb tails on drum hits, high frequency percussion like cymbals, high-hats, solo human voice (we're quite good at hearing unnatural artefacts in voices) - that sort of thing. Beware it has to be good quality source material to start with though!

I used my Pi as an Airplay receiver connected to our hifi. It was pretty bad. But I have a v1 Pi a lot of corners were cut to get it out and under budget for early adopters.

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