Analogue audio quality?

[rrttdd]

Which audio specifications are you aiming for?

For example signal-to-noise ratio, frequency range, distortion...

I wonder if the Raspi could be useful for audio streaming purposes. But that won't be possible if it will sound like grandma's telephone when connected to a hifi rack or better earphones.

[Agrajag]

I could be wrong, but it doesn't appear that this will include any kind of analog audio output; you'd use the HDMI port and get digital audio from that. I suppose you could use a USB sound card of some sort if you need analog out, but then you're limited to the abilities of that external device.

I actually want to use this for audio streaming too, but as a server, running mpd and streaming via the builtin http output or icecast.

[abishur]

Actually, according to Liz over here it will include a 3.5mm jack.

[liz]

Quote from rrttdd on August 1, 2011, 00:12
Which audio specifications are you aiming for?

For example signal-to-noise ratio, frequency range, distortion...

I wonder if the Raspi could be useful for audio streaming purposes. But that won't be possible if it will sound like grandma's telephone when connected to a hifi rack or better earphones.

The analogue audio is, I'm afraid, by no means high fidelity audio. Shouldn't be quite as bad as Grandma's phone, though! It's a DSP-accelerated 1-bit DAC with a low-pass filter.

[Astralix]

Are the I2S channels, together with an I2C routed to the 1.27mm header? That would give the option to add a more sophisticated audio codec on my own.

[eben]

Yes, the I2S is brought out to the header, so you could in theory add a Wolfson or similar. In fact the earlier version of the design (shown in the photos on the site) contains a Wolfson to handle microphone input. A $1 codec looks awfully expensive if you're trying to hit a $25 target price.

[Astralix]

I never argued about not implementing a HiFi codec, it's not target of you design. But it's great, that it is an option to whoever likes it. Wolfson... WM8850 looks fine... only 108dB SNR... may be good for car hifi.

Big question:
Are the extension headers mounted at the fab or are they not placed? Beeing not placed enables the user to decide to which side he likes the headers to stay. So the module could be used easier as a plugin.

[Gert van Loo]

Definitely without connector. So you can decide on your own provided you have the right pitch. We are not yet sure about holes or SMD. Alpha board has holes so you can mount male or female, top or bottom. But holes cost a bit more then SMD due to drill cost.This is one of the feature we have to decide on in the final version.

[JoeBtfsplk]

Quote from Astralix on August 9, 2011, 06:52
I never argued about not implementing a HiFi codec, it's not target of you design. But it's great, that it is an option to whoever likes it. Wolfson... WM8850 looks fine... only 108dB SNR... may be good for car hifi.

Actually 18 bits of audio (noise at -108 dB) is overkill for anything that doesn't have to deal with accumulated error (and much that does.) Only at ridiculously low signal levels could anyone hear any improvement going from 18 to 24 bit. In fact, at normal line signal levels even 16 bits (noise at -96 dB) will cause no discernible noise. Other than for computation with cumulative error or very small signals anything greater than 16 for input and output is hype.

For a mic rather than line input it's another story because mic signals can and often will be very, very small.

So, integrating and coding a WM8850 on a riser would be pretty straightforward? If so, I'm on board for sure.

Can anyone suggest a low power floating point audio DSP that wouldn't be difficult to integrate?

Joe

[johnreed]

I suggest to use a through-hole part for the 1/8" audio connectors. Every quarter, at least one or two students accidentally rip off the Beagle's surface-mount 1/8" audio connectors just by tugging on the headphones cable.

[Gert van Loo]

We have experience with engineers and prototype/development boards. (You can't exactly blame them if they have to test USB installation they have to plug and unplug the USB a hundred times a day.) So all connectors are through hole.

[jgraley]

I'm thinking of getting a WM8850 hooked up too, but the codec chip's interface is HDA, and I can't see that mentioned anywhere on this site. Are the SPI or I2S interfaces compatible?

Also, are there drivers?

PS hi to those who know me