Why do manufacturers use crappy digital filters?

[John007]

Hi, folks. I have my first nos dac and sound is finest i have heard from digital. 20 years manufacturers produce CD players with digital filters which efface fine details in the records. What the hell are doing the engineers in those companies?

[Bernhard]

And for 20 years manufacturers produce CD players with opamps.

[John007]

Not all, fortunately.

[oshifis]

They keep us DIYers busy (we used to describe it as "finishing the manufacturing process")

[Petter]

There are several reasons including:

1. Design for measured performance (which is not necessarily the same as subjective performance)
2. Design for cost (good filters typically cost much more to implement, think die area as one such example)
3. Latency (FIR filters give you latency as a function of their lenght which end users typically don't understand). IIR filters typically require higher precision and better understanding of the problem at hand.
4. Competency of designers (typically math heavy not necessarily audio experts). Indeed, the combination of math and audio seems to be a rarity indeed so the matematicians win.
5. Competency of buyers (often pretty minimal with some notable exceptions, but are they heard in their organizations?)
5b. You can't have your cake and eat it! Tradeoffs must be made and for some reason such tradeoffs are usually made "wrong" on the component level + few have the wish to make the filters themselves for several reasons including competency and cost.
6. Multibit: The process used for the analog output is not very well suited for the digital front end which makes it even harder to meet item 2 above. Trimming etc makes this much much worse again.
7. Low bit depth: Everything is now much easier for the digital designers as they can work on a digital process but that forces other corrections to have to take place.
8. Design for integration (i.e integrate stuff together that doesn't necessarily make sense wrt sound quality)
9. Make tradeoffs to suit specialist applications such as mobile devices, PC's etc. Usually means low power, small size, low cost.
10. Try to "solve" other problems by implementing features not desired for pure sound quality reasons.


Indeed, for those into photography, multibit sensors are analogous to CCD imagers in that the light is captured AND processed in a more "direct" fashion. For CMOS sensors, there is much more processing going on to compensate for operating in the "wrong domain" to begin with (as is the case of single bit or even low number of bit DAC's which are most common these days). Having said that, both methods can achieve excellent results for both audio and photography.

[philpoole]

That's funny. I built a NOS DAC, and when I upgraded it to 4x OS it sounded MUCH better!

I think, in theory, and often in practice, oversampling or digital filtering can improve things.
For the DIYer, NOS is easy to implement. There's no digital filter to interface adding tons of jitter to the signal, and the clock frequencies are very low, and thus easy to use and inherently low in jitter. Also, you can implement unfiltered NOS, to great effect - this is something that obviously can't be permitted in mass production.
So, if you convert to NOS, on a mid priced player, it will most probably be perceived as an improvement.

Also, what DAC did you use, and what was it replacing?


However, if you are careful with your clocks, and ensure that the master clock is low in jitter then I feel oversampling is superior - for obvious reasons.

[peufeu]

After having a non-OS dac for some time I got fed up with the sound.

Digital filters suck only if badly implemented. Which is generally the case.

[petronius]

Beacuse its cheap the first. In audio world is like this you have quantisation noise and it much easy to put digital filter beacuse if you must put some large coils and the you have phase distorsion especially in high frequncies. but I listen in NON Os. Digital filter improve 6dB signal to noise ratio. Transformer in out (to cut all frequencies up to 20000 Hz solve this problem) I dont have but I tr,y results is very very fine.

[Bernhard]

os sounds metallic

[KSTR]

Originally posted by John007
What the hell are doing the engineers in those companies?

Make their product managers happy... or get fired if to insubordinate...

Sad but true (been there, done that).

And still there is some old basic misunderstanding on how correct alias filters should be designed... peufeu already pointed that out.

- Klaus