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L+R channels of my Xonar Essence ST seem to be imbalanced; what to do?, Moved from General Audio (TOS #6)
misha0209
post Aug 18 2011, 17:28
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Hello all,

i have a problem has to do with 0 offset as much as i can figure.

so, i installed clive barker's undying (remembering days of youth tongue.gif) and after using direct 3d mode, not glide wrapper, i experienced something i would not have thought possible in this day and age.my sound output just broke. not that i could not hear anthing, it was more like a very strong SRS effect if you are familiar with it. but irritatingly strong, so strong that you almost could not tell what song is playing due to hissing. so i try to fix, and in the process of uninstalling the drivers i get a nice blue screen (like good ol' win98 - might add the first blues screen i got on win7x64). luckily i had a ghost restore point dated a week before "the happening" so i restore.

all seemed to work well, but it seemed to me that the right channel lacked space, headroom. i own a pair of HD555 headphones, and the sounds in the left cup just seemed to take shape a bit further away from my ear. tried changing balance, thinking it was a volume issue, but sounds in left cup still formed further away, just did not have the same power. then i started swapping left and right channels to see if there is a difference. been doing these things for so long that i actually started to think it was placebo (still not convinced it's not).

so, yesterday i get the idea to record my card's output. and here is what i did:
i generated a logarithmic frequency sweep in sound forge, 44100, mono. then i played back in foobar using my DSP chain. in the chain i resample using SoX, then do 5.1 upmix (by copying, this way i figured stereo input would remain pretty much unchanged), do a huge bass boost, then use a matrix mixer to mix down to stereo. final result, 96kHz, 24 bit, stereo.
now i connected the output of my card to the aux of a laptop and recorded the the sweep - thought aux would be better than mic in because i thought that on the mic in amplification occurred. the megaupload link has 2 files: normal, the 2 channels are identical, at least in windows ouput, and volume change - left 79%, right 80%. sadly the best the laptop could do was 44100, 16bit, stereo. also the laptop was pretty old, so maybe the offset is due to it and not my card.

i can not post the files here because it seems i can not post megaupload links, so here are some pictures:
http://imageshack.us/f/714/97728181.jpg/
http://imageshack.us/f/153/44658577.jpg/

i saved each of the channels in both samples to separate files, and ran foobar track gain on them, and the left channel needed an extra 0.1db attenuation - for normal -. do not know if that is audible.

no what i want to ask is:
is this placebo on my part, and i actually do not hear the difference, 0.1db does seems a small figure?
is this normal - channels not being precisely centered on 0 -?
can anyone tell if this is a Hardware or Software thing? should i risk another blue screen trying to reinstall drivers?
how can this be corrected? can i center both channels to 0, or is this, electronically speaking, as it should be?

Thanks, eagerly awaiting input!
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pdq
post Aug 18 2011, 17:59
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0.1 dB is often mentioned as the threshold below which a difference is not perceivable. However, this is for the same clip played twice at slightly different levels.

If the difference is between right and left channel levels played simultaneously then I don't know what is perceivable.
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misha0209
post Aug 19 2011, 12:09
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thanks, did not know that.

do you happen to know if it is permissible, and to what extent, for a sound card to have differences between channels?

also, i put the sample file on my phone, and recorded it in the same way as from my pc, and the recording has the same 0 offset. so i am thinking it is the cable/laptop i am using to record. sometime this weekend i'll use a different laptop to record the sound card output again, and i will post the results.
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DVDdoug
post Aug 19 2011, 18:42
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FYI - What you are talking about is not "DC offset". You are talking about left-right channel imbalance.

I don't know what's normal for soundcards & headphones, but I doubt you can hear a 0.1dB difference. In the "analog world", things are much worse. Shure's best phono cartridge is specified as <2dB. Certainly, our ears are not perfectly matched. It's normal to for our left & right ears to have somewhat different sensitivity and different "frequency response". (Although, or brains probably compensate so that people with normal-slight differences in each ear don't hear a difference.)

With stereo music the left & right channels are rarely equal anyway. From moment-to-moment, the left or right channel may be louder. It's not uncommon for one channel to have higher peaks, and the opposite channel to have a higher average level. SoundForge might have a tool for measuring peak & average levels.
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misha0209
post Aug 19 2011, 21:23
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my last post may not have been that well formulated.
yes information on channels should be different for stereo, i was talking about the case where i play back a mono file in stereo. technically the result should be identical in both channels, yes?
i think i am talking about dc offset... hope i understand this right. left-right channel imbalance makes me think of the balance control, so volume is involved, volume means increasing peak to peak amplitude, no?
if you look at my second picture, it looks a bit like the first picture in the link you gave me, under DIGITAL DC OFFSET - thanks for the reading material biggrin.gif - though the offset is a LOT smaller.
good to know i should not be hearing the 0.1db difference - helps me convince my brain to stop feeding me lies tongue.gif

This post has been edited by db1989: Aug 20 2011, 17:09
Reason for edit: removing pointless quote of above post
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Rotareneg
post Aug 20 2011, 03:36
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This has nothing to do with a DC offset. It sounds to me like your headphone plug isn't going into the jack on the sound card completely, which will cause a very strange sounding effect, much like what you're describing.
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misha0209
post Aug 22 2011, 12:50
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hi all,

well could not get my hands o something better to record with, but i did record the output of the RCA output of the card, and it looks the same. so does a friend's phone so i'm sure that the problem is in the recording equipment.

on a related note, i find the RCA output to sound better then the headphone output. the amp used in the RCA out is LM4562NA - for the final buffer - replacing the TI6120A2 used for the headphone output. after reading the dataset for the LM4562NA, i see the figure 600ohm load impedance everywhere, but i do not see lower numbers... can someone tell me if i can damage the chip by using lower impedance headphones? - 50ohm, Sennheiser HD598
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pdq
post Aug 22 2011, 13:50
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I have not read the data sheet, but typically it would specify that the testing was done with a 600 ohm load and so the specs are valid for 600 ohms or higher. While the chip is probably protected against damage by a lower impedance load, the specified performance is not guaranteed and will probably be worse, perhaps much worse.
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misha0209
post Aug 22 2011, 14:42
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so the chip should be protected.
i read a lot of forums that people built headphone amps using the LM4562NA, so i could not figure out why the essence uses this chip for line out, and another for headphone (this one is called a high impedance amp by the people @ guru3d in their review, but to me 600ohm on the LM4562NA is damn high impedance).
from a quality point of view, to me, the RCA outputs sound better, more swing, more bass, a bit cleaner separation of instruments.
bottom line is i just wanted to know weather it is, or is not ok to use this output with 50ohm headphones.
thanks!
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