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Audio on a budget: the $9 CHIP computer


mansr
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If you're desperate for some music but only have $9, what do you do? Perhaps you'll buy a CHIP. It has a headphone jack, after all.

 

The DAC on this device is built into the Allwinner R8 system on chip. Without getting expectations too high, we note that it accepts inputs up to 192 kHz 24-bit, and proceed with some tests.

 

Silence is golden, they say. Can the CHIP be silent?

silence-48.png

Reasonably well, it seems. The noise floor takes off upwards around 40 kHz before plummeting again at 50 kHz. The final rise is, at least in part, due to my ADC which is flat only up to 60 kHz.

 

Well then, can it be almost silent? 16-bit dither noise at 48 kHz should tell us.

dither-16-48.png

Uh, what? Why is there a huge spike at 237 Hz?

 

Let's try something slightly harder, a 1 kHz sine wave at -60 dBFS sampled at 48 kHz.

sine-1k-60-48.png

There is a small disturbance at 232 Hz and two spikes at 232 Hz either side of the 1 kHz signal. This repeats around multiples of 1 kHz all the way up to 23 kHz. That is not how this test usually comes out.

 

Enough with the low-level tests. What's the frequency response of this thing?

noise.png

A white noise test shows a reasonably flat output up to 20 kHz and only a slight drop-off above that. Could've been worse.

 

Another 1 kHz tone, this one at 0 dBFS:

sine-1k-0-48.png

A bit of harmonic distortion there.

 

Speaking of distortion, how much of that other kind, IMD, is there?

imd-20k.png

Oh. Maybe it's best to avoid polyphonic music.

 

And then there's the usual j-test for jitter.

j-test-192.png

The side bands are clearly visible, and they get stronger at higher frequencies. Still, not the worst DAC in this respect.

 

Over in the time domain, the impulse response looks perfectly normal:

tek00007.png

Linear phase, same amount of ringing at all sample rates.

 

Square waves are more interesting.

tek00001.png

That's a 1 kHz square wave. Allegedly. Apart from the sloping tops. And the ringing.

 

There is also something very odd going on right around the transitions. Let's take a closer look.

tek00002.png

Whatever that is, it doesn't look right.

 

Lowering the amplitude a little (digitally) makes it go away.

tek00004.png

Maybe it's some kind of arithmetic overflow in the digital interpolation filter.

 

In conclusion, while $9 is a cheap for a 1 GHz single-board computer, audio is best left to an external DAC.

imd-10k.png

j-test-48.png

j-test-96.png

tek00005.png

tek00006.png

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The problem with that $9 chip based computer is that you would need to be a pretty serious computer geek with an advanced knowledge of embedded Linux and general programming skills to get anything out of it. And by the time you put it in a case, add a power supply and video interface and a keyboard etc., I suspect that one would be better off buying a cheap Android tablet (a lot less expensive and easier to program for as well).

George

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The problem with that $9 chip based computer is that you would need to be a pretty serious computer geek with an advanced knowledge of embedded Linux and general programming skills to get anything out of it. And by the time you put it in a case, add a power supply and video interface and a keyboard etc., I suspect that one would be better off buying a cheap Android tablet (a lot less expensive and easier to program for as well).

 

It's no worse than a Raspberry Pi, and people seem quite content to use those (baffling though it is to me).

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It's no worse than a Raspberry Pi, and people seem quite content to use those (baffling though it is to me).

 

Oh, you'll get no disagreement from me on that point. It's just that I would suspect that very few of us could do anything with any of those products you mention. I was just pointing out that it takes a special kind of a computer enthusiast to want to go down that road, and I've found that computer building/programming and audio are not generally companion interests. In fact, I have found that photography seems to be the most common companion hobby to audio, but perhaps in the era of digital cameras and phone cameras being so ubiquitous, that's no longer true.

George

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Oh, you'll get no disagreement from me on that point. It's just that I would suspect that very few of us could do anything with any of those products you mention. I was just pointing out that it takes a special kind of a computer enthusiast to want to go down that road, and I've found that computer building/programming and audio are not generally companion interests. In fact, I have found that photography seems to be the most common companion hobby to audio, but perhaps in the era of digital cameras and phone cameras being so ubiquitous, that's no longer true.

 

I dabble in audio, photography, and computers/electronics. As for the CHIP, I happened to have one (they were giving them out a conference) and figured it would be terrible. Turns out it's not quite as bad as I expected, despite some strange goings on.

 

BTW, did you see Chris' article yesterday about a similar device: Computer Audiophile - Geek Speak: NanoPi Neo, The $7.99 High Resolution Audio Endpoint

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