Should recorded material appear symmetrical? -Sound Forge - PC

Subject:Should recorded material appear symmetrical? Posted by: JHebert Date:10/2/2002 2:59:32 PM Onscreen, when I view the waveform after recording, my waveform is always weighted more toward the upper half of the display, above the centerline. It's as if more data got recorded toward one side, like the signal was low on the other side even though the record meters showed a pretty close balance between L+R. This is not, as far as I can tell, a subtle thing like DC adjustment (especially since DC adjust has almost zero effect on it). However, it seems odd to me when the meters are hitting just about the same peak levels. Would this be normal (I'm guessing not!), a software setting (as in SForge), or a hardware issue (either the driver or the hardware card, the CardDeluxe 24/96)...? It makes me think something's wrong. Is there? And would this affect work I do for anyone else by making audio files that somehow not correct? I suppose I could just set the level hotter on that side, but kind of wanted to ask about it first. James
Subject:RE: Should recorded material appear symmetrical? Reply by: nbedworth Date:10/3/2002 12:00:24 AM Just rip a track from, say, James Taylor's Hourglass, and you'll see that the waveforms are hardly symmetrical. This relates to the absolute phase of the pressure waves coming off the instruments and into the microphone. Now, invert the phase of an Hourglass track, and you'll see how different it looks. Next, listen to it, and it will sound much better. If you can't hear the difference, you need to consider getting better speakers, soundcard and cables... the album, like many, is distributed with reversed absolute phase. Preservation of absolute phase is critical, as it affects imaging, coloration, and of course, transient impact. I can't see your waveforms, so perhaps there is something grossly wrong with things at the electrical level, but otherwise, don't be surprised if the waveforms are fairly asymmetrical above and below zero.
Subject:RE: Should recorded material appear symmetrical? Reply by: Chienworks Date:10/3/2002 2:25:58 PM I think there might be a little bit of confusion going on here too. You mention "centerline", but later refer to the meters hitting the same peak levels. I guess i have to ask if by "centerline", do you mean the 0dB line in the middle of each channel, or do you mean the dividing line between the Left and Right channels? If you're recording in stereo, you will have two waveforms displayed on the screen, the upper one being the left channel and the lower one being the right channel. Both of these waveform displays will contain data above (positive) and below (negative) the 0dB line. The DC coefficient changes how each waveform centers about it's 0dB line, but does not adjust the relative levels between the two channels. The meters display the relative loudness of the left & right channel against each other, but has nothing to do with how much of the signal is negative or positive. A balance control would adjust the relative loudness of the two channels against each other. Now, with this in mind, let me ask if you are referring to the difference between the positive and negative sides of the waveform (most of the live recording i do has much stronger positive peaks than negative ones) or the difference between the size of the left channel waveform and the right channel waveform. I think you mean the former, but your reference to the meters confuses me. The only time you should need to play with the DC adjust is if you see the quietest parts (or silence) NOT on the 0dB line. There is an auto-adjust feature that usually handles this correction quite well. If the silence is centered on the 0dB line and the shape of the waveform is still weighted more to positive than to negative, then so be it. It's still a valid recording and can be played without difficulty.
Subject:RE: Should recorded material appear symmetrical? Reply by: Geoff_Wood Date:10/4/2002 6:22:14 PM Recorded music should appear largely symetrical, with exceptions. However I would guess you have a DC offset in your soundcard. Try the appropriate button in the record dialogue and see what figure that generates. if large, it could indicate and actual ADC fault.

Subject:Should recorded material appear symmetrical?

Posted by: JHebert

Date:10/2/2002 2:59:32 PM

Onscreen, when I view the waveform after recording, my waveform is always weighted more toward the upper half of the display, above the centerline. It's as if more data got recorded toward one side, like the signal was low on the other side even though the record meters showed a pretty close balance between L+R.

This is not, as far as I can tell, a subtle thing like DC adjustment (especially since DC adjust has almost zero effect on it). However, it seems odd to me when the meters are hitting just about the same peak levels. Would this be normal (I'm guessing not!), a software setting (as in SForge), or a hardware issue (either the driver or the hardware card, the CardDeluxe 24/96)...?

It makes me think something's wrong. Is there? And would this affect work I do for anyone else by making audio files that somehow not correct? I suppose I could just set the level hotter on that side, but kind of wanted to ask about it first.

James

Subject:RE: Should recorded material appear symmetrical?

Reply by: nbedworth

Date:10/3/2002 12:00:24 AM

Just rip a track from, say, James Taylor's Hourglass, and you'll see that the waveforms are hardly symmetrical. This relates to the absolute phase of the pressure waves coming off the instruments and into the microphone.

Now, invert the phase of an Hourglass track, and you'll see how different it looks. Next, listen to it, and it will sound much better. If you can't hear the difference, you need to consider getting better speakers, soundcard and cables... the album, like many, is distributed with reversed absolute phase.

Preservation of absolute phase is critical, as it affects imaging, coloration, and of course, transient impact.

I can't see your waveforms, so perhaps there is something grossly wrong with things at the electrical level, but otherwise, don't be surprised if the waveforms are fairly asymmetrical above and below zero.

Subject:RE: Should recorded material appear symmetrical?

Reply by: Chienworks

Date:10/3/2002 2:25:58 PM

I think there might be a little bit of confusion going on here too. You mention "centerline", but later refer to the meters hitting the same peak levels. I guess i have to ask if by "centerline", do you mean the 0dB line in the middle of each channel, or do you mean the dividing line between the Left and Right channels?

If you're recording in stereo, you will have two waveforms displayed on the screen, the upper one being the left channel and the lower one being the right channel. Both of these waveform displays will contain data above (positive) and below (negative) the 0dB line. The DC coefficient changes how each waveform centers about it's 0dB line, but does not adjust the relative levels between the two channels. The meters display the relative loudness of the left & right channel against each other, but has nothing to do with how much of the signal is negative or positive. A balance control would adjust the relative loudness of the two channels against each other.

Now, with this in mind, let me ask if you are referring to the difference between the positive and negative sides of the waveform (most of the live recording i do has much stronger positive peaks than negative ones) or the difference between the size of the left channel waveform and the right channel waveform. I think you mean the former, but your reference to the meters confuses me.

The only time you should need to play with the DC adjust is if you see the quietest parts (or silence) NOT on the 0dB line. There is an auto-adjust feature that usually handles this correction quite well. If the silence is centered on the 0dB line and the shape of the waveform is still weighted more to positive than to negative, then so be it. It's still a valid recording and can be played without difficulty.

Subject:RE: Should recorded material appear symmetrical?

Reply by: Geoff_Wood

Date:10/4/2002 6:22:14 PM

Recorded music should appear largely symetrical, with exceptions.

However I would guess you have a DC offset in your soundcard. Try the appropriate button in the record dialogue and see what figure that generates. if large, it could indicate and actual ADC fault.