ASIO4ALL sound quality

I confirm this: you have to check that there is no sampling rate conversion happening. This is the (only) place where the sound can be altered in such a setup. Except indeed if you applied some EQ (or other FX) in your standard sound card setup.

Thanks for the responses.

Indeed, ASIO4ALL wasn't altering the sound quality. It was due to the high output impedance of my laptop's headphone jack, relative to the input impedance of the headphones I was using. Windows Audio was evidently applying software EQ/other sound processing, and that was masking the effect.

I ended up buying a TDA1308 amp (from IC station for $4), which has an output impedance of 0.25 ohms, and powering my headphones (Sennheiser 558 HDs, which have an input impedance of 50 ohms) with them. Their performance under ASIO4ALL is remarkably better.

For those interested, NwAvGuy has a good discussion on the signal filtering that can occur with high amp:headphone impedance ratios here: http://nwavguy.blogspot.com.au/2011/02/...dance.html

Headphones are usually the weak link in the chain rather than what's driving them. Have you tried other earphones and got the same sense of muddiness? Trying a range of headphones is really the starting point here.

Unless you have some sort of audiophile internal sound card the card you have will indeed limit your SQ, but the effect will be more subtle than the differences between one set of headphones and another. You will tend to notice this as the weak link in the chain only after you settle on a set of good headphones. Then IMHO the next best option is to bypass the internal card, use one your your digital outputs, and run it to an external combination DAC and headphone amp. That should suffice unless you want to go for that last 1% of SQ. Then you'd add a high end standalone headphone amp after the DAC.

Ah, simple to clarify: a DAC at a minimum has one digital input and one set of analogue outputs. In this minimum configuration the outputs are line outputs, intended to drive a preamp. They won't drive most headphones, and in this configuration there is no internal volume control.

A lot of 'DACs' however offer more than this. One common option is to include a headphone amp inside the box, along with a volume control for it. [The line outputs are maintained also.] I was more or less assuming that you were thinking of such a combination  DAC/headphone amp configuration. It is a nice, clean, effective option.

My comment arises from the fact that really serious, last 1% headphone amps are almost never found in DAC/headphone amp combos. In my own case I have a pretty high end DAC/headphone amp combo driven by my piano VSTs and other sources, a Yulong DA8. I find the headphone amp in iti just fine in most cases, but  while good, it does not quite measure up to the two external headphone amp options I can use.

I'm not sure of a way of quantitatively diagnosing this without an oscilloscope. If you have one, you could send a sine signal via your sound card to your headphone jack/amp (e.g., you can do that in Audacity with the tone generation utility), and measure its amplitude by connecting the oscilloscope across your headphone jack/amp. Then, look at how the amplitude of the signal varies with frequency of the sine wave. If the amplitude varies by orders of magnitude as you sweep the frequency between ~ 50 Hz and ~ 20 kHz, chances are the source signal's being filtered somewhere.

Though as I mentioned in the above post, I just ended up getting a cheap TDA1308 amp (which has an output impedance of 0.25 ohms) to power my headphones, to test if filtering was occurring in my laptop headphone jack -> headphone setup, and could easily hear the difference. The mids dropped, and the bass and highs rose, making the sound seem much less muddy.

I'd second what NormB said here about trying a variety of different headphones (being sure you're not using an amp that results in a filtering of the signal, and maybe also using it with an external DAC), and only then changing PTQ presets/parameters. For what it's worth, I currently use a pair of Sennheiser 558 HD's with the TDA1308, and am generally pretty happy with their PTQ performance.

Interesting - how'd you measure the output impedance of that laptop port (that might also answer AlexS's other question)? I guess the relatively high output impedance of the line out is consistent with it providing a relatively low current (and hence power) compared to a headphone amp.