Computing stuff tied to the physical world

Posts Tagged ‘Audio’

Audio DAC

In Hardware on Jan 11, 2013 at 00:01

Last year, I got one of these little low-cost audio Digital-to-Analog Converters on eBay:


Takes digital SPDIF coax in, and produces analog left and right channels out. I got them before the bigger picture of the audio chain in the living room got fleshed out, and in the end I don’t really need this type of converter anymore.

Besides, there was some hiss and hum with these, so it’s not really high-end anyway.

Here’s what’s inside:


That’s a Cirrus Logic CS8416 “192 kHz Digital Audio Interface Receiver”, which apparently has all the smarts to detect and decode a range of serial bit formats, plus a Cirrus Logic CS4344 “10-pin, 24-Bit, 192 kHz Stereo D/A Converter” to generate the L/R audio signals.

I’m a bit surprised by the hiss/hum issues, since the audio DAC is specified as -90 dB THD+N and 105 dB Dynamic Range, which to me sounds like it should be pretty good. Maybe not audiophile level, but hey… neither are my ears, anyway!

The world of audio

In Hardware on Dec 13, 2012 at 00:01

There’s a huge world out there which I’ve never looked into: audio. And it has changed.

It used to be analog (and before my time: vacuum tubes, or “valves” as the British say).

Nowadays, it’s all digital and integrated. The common Class-D amplifier is made of digitally switching MOSFETs with some cutoff filters to get rid of the residual high-frequency this generates. Leaving just the “pure” audible portion to drive the speakers.

With the recent switch to a new small TV, away from the Mac Mini, for our TV & music system, I lost the original hook-up we had, which was a (far too cheap) little analog amplifier driving (far too expensive) speakers we’ve had here for a long time.

So now we have this TV with built-in tiny 2.5W speakers blasting to the rear – a far cry from the sound we had before. And no music playback capability at all in the living room right now. Not good!

Our needs are simple: CD-quality music (we’re no audiophiles) and decent TV sound. I am going to need a setup soon, as the Christmas vacation time nears.

Trouble is: the sound source for our music is on the Mac Mini server, which is in an impossible place w.r.t. the TV and the speakers. So my first thought was: an Airport Express. It can play over WiFi, and has optical audio output. But… the AE draws 4W in standby. And turning it on for each use is awkward: waiting a minute or more to get sound from the TV is not so great.

The other options for music are an Apple TV or a specially-configured Raspberry Pi.

The only remaining issue is how to get sound from line-level analog audio or (preferably) digital audio to the speakers. I ended up choosing something fairly simple and low-end, a component from miniDSP called “miniAMP”:

DSC 4302

This takes all-digital I²S signals and produces 4x 10W audio. It needs a 12..24V @ 4A supply, i.e. a simple “brick” should do. But that’s just half a solution: it needs I²S…

This is where the “miniDSP” component comes in (the SOIC chip at the top is a PIC µC):

DSC 4301

So the whole setup becomes as follows – and I’ll double up the miniAMP (one for each channel) if the output is not powerful enough:

Screen Shot 2012 12 12 at 23 11 57

The miniDSP takes 2x analog in, and produces up to 4x digital I²S out. The nice part is that it’s fully configurable, i.e. it can do all sorts of fancy sound processing:

Screen Shot 2012 12 12 at 23 21 17

This is perfect for our setup, which includes old-but-incredibly-good separate speakers for the highs and the lows. So a fully configurable cross-over setup is just what we need:

Screen Shot 2012 12 12 at 23 23 11

The way this works is that you set it up, burn the settings into the DSP front-end via USB, and then insert it into the audio chain.

It’s tempting to start tinkering with this stuff at an even lower level, but nah… enough other things to do. Although I do want to look into auto shut-off at some point, to further lower power consumption when no audio is being played. But for now this will have to do.