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Using Audacity to do NOS droop correction

Posted 29th April 2012 at 03:36 AM by abraxalito

If you have a NOS DAC (like a Metrum) and are curious to hear how it sounds with the zero-order hold corrected, here's a fairly simple way to try out my 3-tap filter using Audacity.

Load up the file you'd like to process and make two duplicates (select original and use Ctrl-D) - we'll call them A and B. We need to apply delay and gain to A and B which we do with Audacity's time-shift button (in the group of 6 tool buttons to the right of the transport buttons) and the 'Effects - Amplify' feature. A is shifted one sample to the right, and B, two samples right. I've shown how this looks with a mono chirp signal in the first image.

The gain is input into Audacity in dB so 0.15 becomes -16.5dB and 0.026 is -31.7dB. These are the gains for A and B, respectively. A needs to be inverted too - use 'Effects - Invert'. The second screen grab shows how it looks after these operations (I hid the device toolbar to give more space for waveforms).

Having processed...
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First measurement of NOS droop correction

Posted 27th April 2012 at 06:13 AM by abraxalito

Here's a ten discrete tone test waveform played back into my Sony PCM-M10 then FFT'd in Audacity with 512point FFT.

Audacity reports lower freq tones at -18.6dB and the highest (17.3kHz) at -18.9dB - a droop of 0.3dB. This might be in part my passive (LC) reconstruction filter which I have yet to characterize separately. So it appears to work
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Flattening the NOS droop

Posted 14th April 2012 at 03:13 AM by abraxalito
Updated 14th April 2012 at 03:48 AM by abraxalito

Having been a fan of NOS DACs now for something over a year I've decided it was high time for sorting out their most serious drawback - the roll off in the HF. This is an unavoidable result of using a zero-order hold function to reconstruct the original (impulse) samples. Droop exists even with oversampled DACs, its just at its most severe in NOS.

One of the most popular ways to flatten the response is to add on some kind of analog filter with a rising response (to 3.16dB @ 20kHz). A first order shelving filter can't quite cut it though so an LC tank circuit has been employed by a few. This needs to have a moderately high Q to achieve the correction.

I've played around with inductors to achieve this and haven't much liked the resulting sound. Whether this was due to the particular inductors I was using I didn't experiment. Admittedly they were very cheap ones. In general though when I've used high Q circuits in crossovers I haven't much liked the colouration...
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ARM's cutest baby now has an even less hungry sister

Posted 16th March 2012 at 02:45 AM by abraxalito

Cortex-M0+ Processor - ARM

Just 11uW/MHz at 90nm so under 1mA current draw when running at 100MHz Freescale says they'll be first to show working silicon but I bet NXP will end up shipping the real volumes.
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The end of Moore's law

Posted 26th February 2012 at 05:28 AM by abraxalito

Of late I've been enjoying snacking on this book EDAgraffiti which is a romp through various aspects of the economics of semiconductors. Recommended for those who are interested not just in the technical side of the digital revolution but also the commercial perspective too.

One comment from the book jumped out at me, which was a prediction made by Clayton Christensen a few years ago about the end of Moore's Law. He's reported as saying the following at an engineering conference organised by Cadence. Moore's Law will come to an end when the semiconductor industry tries to deliver more capability than the mainstream requires at a price which is higher than the mainstream wants to pay. 450mm wafer processing technology and EUV lithography pretty much do seem to fit the bill here.

This article on The Inquirer is saying pretty much the same thing - gaming and video transcoding have kept the push for faster PCs alive but even in those applications demand is now...
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Anyone notice parallels here with Intel?

Posted 23rd January 2012 at 01:25 AM by abraxalito
Updated 23rd January 2012 at 01:27 AM by abraxalito

Could Kodak's demise have been averted? | Technology | The Observer

My best bet for why Kodak is history comes towards the end of this relatively short piece:

More insightful analyses point to the fact that Kodak had a near-monopolistic grip on a market that was giving it a 70% margin on its products and processes, and that therefore the people who ran the film part of the business were the ones who carried most weight in corporate discussions.
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Interesting blog post about fake chips

Posted 3rd December 2011 at 04:27 AM by abraxalito
Updated 5th March 2012 at 03:50 AM by abraxalito

On Counterfeit Chips in US Military Hardware bunnie's blog
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The Von Neumann architecture is becoming the niche.

Posted 15th November 2011 at 03:50 AM by abraxalito
Updated 5th March 2012 at 03:51 AM by abraxalito

https://garysmitheda.com/paper/ARM-Techon-note.pdf

Its a single page review of ARM Techcon. At the end I think he means 'PC design' not 'PCB design' as he's written.

He says:

If Intel doesn’t do something soon this might not be much of a war.

He knows some guys at Intel read his analysis so I think he's sugaring the pill. Intel is rather like the hare in the old fable of the tortoise and the hare. The hare woke up and tried to catch up with the tortoise but it was too late. That's exactly where Intel is right now - they've become awake to the issue but they've missed the boat.
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A man with cojones...

Posted 27th October 2011 at 08:33 AM by abraxalito
Updated 5th March 2012 at 03:49 AM by abraxalito

How often are you likely to read the words 'Jobs eventually relented' ? Read and weep Intel; Tony Fadell: respect.

Steve Jobs Wanted Intel Chips for the iPad - Digits - WSJ
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What's in a datasheet?

Posted 7th October 2011 at 05:38 AM by abraxalito
Updated 14th November 2012 at 02:47 AM by abraxalito (Updated with link to new article 14th Nov 2012)

Yesterday I had this very interesting exchange with RocketScientist about his open source design for a headphone amp, the O2.

https://www.diyaudio.com/forums/headp...ml#post2736266

The nub of the issue raised here is - should designers stick only to what datasheets tell them about parts or to what extent use what's 'common knowledge' about parts to eek out better performance?

I was surprised to learn from RS that offsets within dual opamps are so closely matched in practice - its a really new discovery for me. So why don't semiconductor manufacturers tout this feature? Or perhaps RS just 'got lucky' with the relatively few samples he tested?

My experience of reading opamp datasheets is that the specs for offsets (both the typicals and the max) degrade in going from single to dual devices, where the devices are all on one die. Let's have a look at a relevant opamp from...
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