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RE: Digital -still improving

Hi,

> With some DACS claiming (and apparently getting) -140db,
> there was still work to be done.

Forgive me for injecting any reality into this.

Given that the quietests microphones known to man have around 9dB(A) self noise and many recording microphones exceed 20dB(A) and given that a classical orchestra in a full tutti in the front rows rarely exceeds 105dB SPL, what is the use of very large SNR figures (I mean except for advertising)?

I would suggest that anything that betters around -110dB SNR is good enough to not represent a limitation on the basis of noise levels for real recorded music. It does no harm to have a few more dB, but I would not class it as a valid engineering goal to pursue SNR levels much past 110dB.

The issues are elsewhere, in the digital filter charateristics, the noiseshapers used (generally i find higher order noise shapers not very nice) and supersonic noise signature of DAC's.

> About 10 years ago, the Burr-Brown 1704 (converter-chip)
> disappeared.

About a year ago it remained in production, though it now has a pricetag of the "if you have to ask..." variety. It has since been discontinued because TI closed a FAB that did this sort of Job.

Lucky their hybrid DAC line was not affected. Too bad for their competitors that TI still has valid and non-expired patents on that tech. The nice thing is, with 6 Bits in multibit any noise from noiseshaping of the lower bits is pushed down 36dB at all frequencies. No Delta Sigma system can match that.

> Then, the AK 4490 - a new chip from the orient. ... -and
> it could be a breakthrough.

Don't see how.

AKM and Cirrus Logic used to share technology closely. Both their DAC lines continue to use switched capacitor systems which makes them dirt cheap but not particulary distinguished. The AK4490 is a decent DAC chip at a keen price, but not really materially better than the competition from Cirrus Logic.

Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

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