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Noise modulation and subjective performance of DACs

Posted 25th December 2012 at 05:22 AM by abraxalito
Updated 20th September 2014 at 03:41 PM by abraxalito

I've recently come to the view that the best metric of SQ in DACs is noise modulation, however as yet I'm unclear how best to go about making the measurement. Stereophile tried, and here's what they did - Noise, Modulation, & Digital/Analog Conversion | Stereophile.com

Robert Harley reports no correlation with listening so I deduce from this that the test method isn't looking for the right thing. My own gut feel is we need a multitone test waveform rather than a single sinewave as a sinewave has a crest factor quite unlike music and if a sine provoked the condition we'd see it on the 'N' part of a THD+N vs level test.

Having said that, of course we do indeed see something weird going on - on Weiss Medea's implementation of the ESS Sabre. The THD+N plot versus level shows kinks which most certainly are not increased THD at various levels, so can only be noise floor modulation. See a critique I made on WBF here - http://www.whatsbestforum.com/showth...l=1#post133677...
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Digital that sounds like analog

Posted 10th December 2012 at 04:18 AM by abraxalito
Updated 15th February 2013 at 06:11 AM by abraxalito

For those who missed Frank (fas42)'s link on a thread I started then here's where I'm continuing my minimal oversampling DAC developments for the time being : Digital that sounds like analog
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NXP's innovation in smart phone sound - any implication for the high-end?

Posted 2nd August 2012 at 05:13 AM by abraxalito

EET seems to be on a run of interesting articles of late - and here's the latest, about NXP's latest digital amp for smartphone speakers:

Achieving loud, rich sound from micro speakers

So yeah, smartphones are a long way from the high-end you say, so why talk about this at all? Well one sentence at the end caused me to pause and wonder how long before this kind of technology gets used where sound quality (rather than quantity) is paramount. I quote:

This leap in performance illustrates an important design trend. The days of stand-alone amplifiers and converters designed in isolation have gone.

The writer has put his finger on a major reason why the high-end of audio is a relatively stagnant pool for innovation. Pretty much everything's designed in isolation - players, amps, speakers. What if those days really are coming to an end, not just in smartphones but in quality audio too? Smartphones have the volume so there's economic...
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Cirrus now Apple's poodle

Posted 1st August 2012 at 04:53 AM by abraxalito

Cirrus (familiar to us in the audio world as a major ADC/DAC and codec supplier, formerly Crystal Semiconductor) has engineered itself into a tight corner by having over half its sales come from Apple - but its not permitted to mention its largest customer by name due to Apple's draconian NDA.

I wouldn't say things are looking very bright for Cirrus - to be that dependent on one single customer who is that much more powerful than you and a known corporate bully strikes me as poor strategic thinking.

Apple captive Cirrus gagged
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Insider story on Intel's FinFETs - allegedly...

Posted 27th July 2012 at 05:00 AM by abraxalito

Here's an interesting article where Warren East is commenting on ARM's competition with Intel. But for the sting in the tail, scroll down to the comments. The first one appears to be from an Intel insider - fascinating stuff. Let's hope it doesn't get pulled

ARM, TSMC lead Intel in SoC, says CEO East

He (nc3) says :

Intel's 22nm also has much higher leakage, cost, worse analog, worse RF, worse high V transistors in terms of specs and the type of devices offered.
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Nvidia wants a divorce from TSMC?

Posted 18th July 2012 at 03:08 AM by abraxalito

This article is a fascinating peep behind the curtain of the current economics of semiconductor production through the eyes of a major IP player - Nvidia. More evidence that Moore's Law is grinding to a screeching halt I suggest.

Nvidia deeply unhappy with TSMC, claims 20nm essentially worthless | ExtremeTech
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Mathematics of DAC droop correction

Posted 29th June 2012 at 05:09 AM by abraxalito

Here's one of the clearest articles I've seen which explains the background and a couple of solutions to DAC roll-off.

Flatten DAC frequency response | EDN

Both the solutions proposed compromise the dynamic range. My own solution, a hybrid analog/digital approach relies on DACs being cheap - I've termed it 'LAID' which stands for 'Longitudinal Array of Inexpensive DACs'.
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Prototype MOS DAC

Posted 23rd June 2012 at 08:22 AM by abraxalito

The prototype is listenable now, but a bit too much background noise/hum pickup to do serious listening. It needs an on-board post filter and amp, which I'm working on now. In the meantime, here's the pics - the DAC itself is built of 5 'dac-sleds' each with a stack of 4 chips. The 'sleds' are then arranged around the central tower holding the resistor ladder. A separate board handles the timing logic and 18 tap delay line.
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Evolving NOS -> MOS

Posted 9th June 2012 at 07:13 AM by abraxalito

Fixing the NOS droop has the undesirable side-effect of making the imaging components worse - HF gain can't be increased up to 20kHz and then suddenly taken away above 22kHz

In the spirit of taming the near-ultrasonic emissons of a NOS DAC, I'm currently playing with an MOS design - where 'M' stands for 'minimal'. I've been wondering if the attractiveness of the NOS sound will still be preserved if I go to 2X OS in order to fix up the ultrasonics. No practical analog filter can have a sharp enough band edge so a digital one it does have to be...

A DSP implemented digital filter comes at a price - that of throwing away some bits (I'm still using only 16bit DAC chips - TDA1387) so I'm now exploring using a transversal filter (no DSP) to carry out 2X OS. The LTSpice screen grab shows the architecture I'm playing with - a 19 tap delay line feeding 19 separate DACs. The DACs are shown on the right as current sources and their individual weightings are...
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DACalito - transversal modification of DAC-AH Lite

Posted 30th April 2012 at 06:46 AM by abraxalito

Plenty of audio DIYers have discovered what an excellent modding base the DAC-AH Lite is. I'm a latecomer to the party, but better late than never here's my contribution to the art of DAC-AH-alikes.

Most of the mods I've seen focus on the output stage, some upgrade the PSUs. Here's yet another variant - change the DACs. The TDA1545 is pin compatible with the TDA1543 so I swapped out 8 TDA1543s and replaced them with 8 DAC-stacks made up of 5 TDA1545s each. 32 DACs in parallel produce the normal NOS output, the additional 8 DACs are fed from a two-stage delay line (16 74HC595s) to correct for the zero-order hold. I/V conversion is done passively and differential - 1.3ohms in each polarity. The post I/V stage is a pair of AD605s giving a true differential output. In between the two is a passive filter made up of TDK ferrite beads and NP0 capacitors.

How does it all sound? - well of course one is always biassed when describing one's own offspring, but in a word...
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