Xonor STX Line-In Mods

[kenwood850]

Interesting discussion, but I think it is time for me to bow out. 5th element, thank you very much for taking the time to explain a few things to me in your last post in response to mine. After your comments about the Line-In input not being as sensitive as I was suggesting, I went back and found the post. It is here

http://vip.asus.com/forum/view.aspx?id=20090519034729846&board_id=21&model=X onar+Essence+STX&page=1&SLanguage=en-us

or here

http://tinyurl.com/6wp6r33

After reading it a second time I noted in his second post further down the page that he back pedaled a bit so apparently you are right.

It is too bad you and phofman were not on the design team for the STX. It might have turned out to be a much better card for those looking for a good line-in input. On the other hand the bean counters would probably have still won in the end. Such is life. Thanks again.

P.S. I finally heard from Asus and their only suggestion was to RMA the card if I thought there was a problem. They either don't get it, or they are choosing not to get it.

[5th element]

There's no doubt that the line input on the Xonar is very high quality, I use it to perform measurements and Stereophile's own measurements of the card only back up how vice free it appears to be. Sure you can do better but only if you really want to spend high.

The fact that the ASUS does not provide any gain on the input is really one of minor consequences and is certainly not any fault of the original designer. Having the ADC reach 0dBfs when fed with a 2Vrms signal is the standard and usually it is better to follow standards, rather then to ignore them.

Now as to your problem, what kind of level issues are we talking about? If you record something with Audacity for example, how much gain can you apply without clipping the signal?

Aside from that though record players don't tend to deliver particularly high signal to noise ratios. The ASUS, from my use reaches around the 120dB mark which is nearly as good as it can get, the input stage is very quiet. If you were to make a recording from a record that has a signal to noise ratio of 70dB, then you'd be free to apply up to around 50dB of gain in audacity before the cards performance starts to contribute.

If the peak level on the record reaches -30dB on the digital scale, the noise of the record would lie around -100dB. If you applied 30dB of analogue gain before the card, so that the peaks hit 0dB, the noise would hit -70dB. In both situations the card would accurately capture the signal applied to it. If you use analogue gain before the card, or digital gain after it, the end result would be the same, a noise floor of -70dB as dictated by the vinyl medium with the audio reaching peaks of 0dBfs.

[phofman]

I finally found linux amixer list of STX controls https://launchpadlibrarian.net/95171...xer.values.txt These controls show real hardware capabilities as the guy who wrote linux STX driver has access to Asus documentation for the card. There is no line input gain control listed, only the mic gain. The side input aux connector offers gain control but that is just an auxiliary feature.

[kenwood850]

Originally Posted by 5th element

There's no doubt that the line input on the Xonar is very high quality, I use it to perform measurements and Stereophile's own measurements of the card only back up how vice free it appears to be. Sure you can do better but only if you really want to spend high.

The fact that the ASUS does not provide any gain on the input is really one of minor consequences and is certainly not any fault of the original designer. Having the ADC reach 0dBfs when fed with a 2Vrms signal is the standard and usually it is better to follow standards, rather then to ignore them.

Now as to your problem, what kind of level issues are we talking about? If you record something with Audacity for example, how much gain can you apply without clipping the signal?

Aside from that though record players don't tend to deliver particularly high signal to noise ratios. The ASUS, from my use reaches around the 120dB mark which is nearly as good as it can get, the input stage is very quiet. If you were to make a recording from a record that has a signal to noise ratio of 70dB, then you'd be free to apply up to around 50dB of gain in audacity before the cards performance starts to contribute.

If the peak level on the record reaches -30dB on the digital scale, the noise of the record would lie around -100dB. If you applied 30dB of analogue gain before the card, so that the peaks hit 0dB, the noise would hit -70dB. In both situations the card would accurately capture the signal applied to it. If you use analogue gain before the card, or digital gain after it, the end result would be the same, a noise floor of -70dB as dictated by the vinyl medium with the audio reaching peaks of 0dBfs.

First of all my apologies for not responding to your post sooner.

What you have said makes sense and I also did some follow up of my own. I found the paperwork that came with the preamp and it indicated that the preamp has a maximum output of 1.4 Vrms. In theory that is 70% of the maximum input level of the card. I wasn’t seeing values that high in Audacity but my guess is that I had the preamp adjusted down from the maximum value to make sure I was avoiding clipping in the preamp. At this point I stand corrected on the cards performance and my choices are another preamp with more output or amplify it after the recording session in Audacity. Based on what you said the advantage would be to do it in Audacity. It saves the expense of another preamp and I will never have to worry about clipping occurring during the actual translation from analog to digital. Thanks again for taking the time to respond.

[5th element]

You're welcome.

I think it is also perhaps worth pointing out that analogue and vinyl are slightly different from digital when it comes to absolute signal levels. Digital is extremely easy as the maximum possible equals data encoded at 0dBfs on the digital medium. As a result of this it is also easy to define guidelines on what a 0dBfs signal should represent in the analogue domain. In this case 2Vrms is the standard.

With a record this isn't quite the same, I am sure there is a size that could be cut into a groove that would represent something of a maximum, but the trouble here is that some styluses might be okay with a certain groove size, whereas others might jump the groove etc. Then coils come in all sorts of different types and sensitivities, making it difficult to define an absolute maximum. In this regard you could monitor the output of the preamp and find that with 10 records the signal doesn't clip and set the gain accordingly, however on playing back an eleventh record you find that it does clip.

It makes sense to err slightly on the side of caution, by keeping the pre amps gain lower, so as to have more headroom available should you encounter a record with higher then average peak levels.