Apparently the DAC for sale here is making big waves in the 'audiophile' communities:

http://ack.dhs.org

To make a long story short, it's a battery powered non-oversampling external DAC with no filters. The claim is it sounds more "analog like" than most DACs. Perhaps this is not a new thing, but new to me anyway...



Seems like a weird design to me (never mind that you get about 4 to 6 hours of battery operation, then have to charge it for 8 hours!). Can anyone comment on this sort of "purist" non-oversampling non-filtered concept?

Yeh, it works (well non-oversampling at least) For me at least. I converted my old rotel 855 using a TDA1541 multibit dac. Very easy just cut 3 pcb tracks and reconnect 2 3 diff pins. This DAC (in double crown version) was recently used by Marantz in their statement CD7. Audionote UK have been using non-oversampling DACs for sometime. Not sure about this particular DAC but using batteries is a good plan (though i personally would go for some nice large Yuasa lead acids to get some good operational times)

Interesting... non oversampling and no filters whatsoever, isn't that asking for some digital noise (or am I way off base... guess I really don't know much about DACs, and this one looks like one of those strange snake-oily designs). Why would this not be done commonly, if it were an improvement?

No, you still have an analogue filter (its ultra sonic output and digital images - i suggest you read up on the web - google is a great thing), you just have to re-calculate it (although some dont and you may get away with it). Most cd players analogue filter is an op-amp based affair. It all depends on what it is you want and how far you will go. Most cd players do sound artificial compared to a decent (well engineered) record deck. Its widely accepted here that upsampling 44.1 to 48khz soundcards are not as good as straight through cards - you can look on this in a similar manner (not really a good desc but you get the idea - simpler is better). The original reason for a digital domain filter was to decrease the need for a complex analogue (read more expensive) one. Turns out you dont need it. I was sceptical, but ive checked it out and it works for me. Im asembling a second system around it cheaply - could well end up better than my main system.

edit: think main reason is compatibility reasons - its difficult to design it so that it will work correctly all the time with existing amps. Also most might not be able to tell the difference - doesnt mean it isnt there though. Most people have no idea just how amazing stereo can sound - its just that you have to have a chair in the right position and the speakers situated correctly etc etc (bad acceptance factor in the home) - then and only then will you hear what the music is really doing (soundstage, imaging etc). But at the end of the day i always say if you are happy then thats all that matters.

In theory, non-oversampling DACs are no good at all. In practice they work reasonably well, but cannot match well designed 1-bit DACs. (the fact that the PR mentions "tonal purity" says more than enough )

http://www.diyaudio.com/forums/showthread....t=&pagenumber=1

Menno

As with everything. Everyone is entitled to their opinion. I dont currently listen to non-os. I listen to a 10 year old bitstream cd player. Because I like the way it makes music.

Before 1990 they used to make the best sounding gear & the best overall value (I can afford). Too bad that I have to find a cd player with variable out (I hate preamps

Questionable However you'd have to listen to one to decide if it sounds better (it will sound different for sure, god knows if more accurate).
Not for me anyway (I have ribbon tweeters flat up to 32kHz and the thing would kill them due to garbage over 21kHz).

Any brand names you could provide, for a possible hunt on eBay? Been thinking about putting together a small bedside listening station...

Lots of Marantz models are good: CD80, CD94mk2. Rotel have made some very good ones (IMHO). Depends what you like in your music - the early bitstream models are a bit weak in bass drive, but have good voices, to me at least. The variable out on most players is not much cop. Much better to use a transformer based volume control as this is the most transparent method (better even than a stepped attenuator) Sowter make them and Stevens and billington.
http://www.sowter.co.uk/attens.htm
http://www.stevens-billington.co.uk/pagehifi.htm

I want to get me one of them!

Grab an decent old cd player, upgrade the clock (there are some cheap ones about if u look). Shove in some better op-amps and some better caps in the power supply/decoupling. Add a seperate transformer for the output secton and put in a couple of transformers for volume control. Hook it up to any decent power amp and away you go. Shame im so skint....

Shame my soldering and electronics DIY skills are either rusty or nonexistent at this point...

P.S. this is the first time in my life I've ever heard of anyone using a transformer for volume control. Never once seen it in a piece of equipment before either, as far as I know. What's the problem with a stepped attenuator? (I can see the minor issues using a pot, but can't even imagine one using fixed resistors for attenuation).

What about this: If input impedance isn't constant (= different depending on frequency), using a resistor for adjusting volume (= increasing output impedance) can result in a changed (non-flat) frequency response. I have no idea if this can be a problem in practice.

Im not too sure on this one myself. Ive not heard one. But there are products that use them. One of the main problems with a passive preamp is the lack of dynamics compared with an active one. These are supposed to be better in this area as well as others. Its based on induction instrad of resistance. To be honest the results would probably only be audible in a already very good system. This is one of my pipe-dreams if you like - one day.......

Ehm... transformers are passive devices too, and are prone to create much more problems than simple resistive attenuators: low frequency distortion, poor frequency response and noise pickup. Transformers are used in high-end audio just at tube amp output stages, in order to decrease amp output impedance. There's no need to use them with line-level devices or low output impedance solid state amps, unless you want some coloration or distortion added by a transformer.

Also, non-oversampling DACs are just prehistoric DACs, in a similar fashion to first 14-bit DACs. Oversampling was adopted as a method to implement much more cheap and effective anti-imaging brickwall filters, compared to previous, expensive, poor performing analog brickwall filters.

But it seems that the DACs advertized lack any filter at all. Those are incomplete DACs. The lack of a anti-imaging reconstruction brickwall filter will lead to a signal full of garbage over fs/2 or 22 KHz, consisting of reflected images of the original baseband signal, just where there should be nothing. This can lead to intermodulation products caused from this ultrasonic garbage to fall into the audible band, because some equipment is not very linear at ultrasonic frequencies. In best case, this won't happen, and there will be no detrimental consecuences if using these kind of DAcs. But it will offer no benefits at all, compared to well-behaved oversampling DAC with proper anti-imaging filters (note that all music recorded at a CD has been already brickwall filtered over around 21 KHz, at the ADC stage).

As to


these are just plain false facts, or in other words, this is marketing BS.

BTW, there was an old post abouth these kind of filterless DACs, but I can't find it now.

Hey - I agree with KikeG!


The last thing you'll get is purer tonality. You will get a shorter impulse response, but that's not a good thing: it's totally artificial.


The impulse response is only "accurate" if you combine it with the low pass filter in a human ear. If you analyse it properly (i.e. generate near-impulses in the analogue domain, convert them to digital, and then back to analogue using this device) you'll find that the impulse response is terrible: it will be amplitude and width modulated depending on how the "impulse" aligns with the individual sample(s).

The amplitude and width of identical impulses using a brick wall filter is identical (as it should), and is not affecrted by how they align with individual sample(s).


Cheers,
David.

That's where the debate seems to lie. Proponents of unfiltered, non-oversampling DACs (clearly a fringe sort of thing) claim that in theory they should sound worse or the same, and in practice they sound "better."

Never having heard nor tested one, I have no opinion but find the topic interesting anyway... why would people claim there was something audibly better about this sort of DAC? It's tempting to say "marketing" or "audiophile voodoo" and leave at that, but imo these things at least deserve investigating rather than dismissal...

It states:But this could be a simple analog filter to me
I agree that non-oversampling shouldn't give more tonal purity.
--
Ge - trying to make some sense of it

First, they should prove they really sound different. If they do, something that could be possible (I think the difference would be subtle in most cases) then their "better" sound would be something totally subjective: it would be like saying that lossy compression degradation, or 14-bit DACs, giving two examples, sound "better". For some people it may, for some people it won't, but in any case, that's not what I aim for when listening to music.



For the reasons explained, I think of the first as the most likely.

Yes... so do I. Nevertheless it would be interesting to hear one of these DACs I mentioned in the first post, although I'm not spending any money...

As far as proving differences, I don't think most 'audiophiles' are interested in that... rather, the interest is in believing that something sounds better for some subjective reason (price, looks, weight, brand name, social consensus, ownership pride, or even just as an excuse to keep playing with different audio toys on a regular basis). Anyway, that's my observation from spending so much time at the head-fi forums...

According to that quote, it's a first order (6 dB/octave) analog RC filter, which is totally useless for adequately rejecting ultrasonic images.

Not to say that, for the intended use in this context, the precision of the resistor at the filter is not critical at all. It seems that all that counts is the marketing language, in order to fool as much people as possible.