Ralf, you have been engaging heavily in this discussion, but, as it seems to me, with increasing aggression. I cannot comprehend that - if you do not like my idea, you do not have to use it. Further comments below. Am 24.08.2015 um 11:55 schrieb Ralf Mardorf: > On Sun, 23 Aug 2015 18:07:32 -0700 (PDT), Bill Unruh wrote: >> Now, that may mean that there is common mode noise, in which case >> running the balanced into an unbalanced would be very noisy, or the >> noise was all in the ground wire, in which case bal->unbal might work. > It's the nature of unbalanced connections, that they are noisier than > balanced connections. That's why I'm trying simulate a balanced one - before you go bananas now: If you look back to my initial message, you'll notice that I used the words `abuse' and `experimental' to describe my approach. > > However, there are several ways to implement balanced IOs. Using two > unbalanced mono input channels as a single balanced input channel is > not one of that ways. That must be why that way works well, as it seems. > > Most important is that the output and input fit together, than to care > about balanced or unbalanced. Cable length and impedance need more > attention. > > The microphone might provide line output (unusual, but not impossible). It does - not very loud, but there is a clear signal when recording through the line input - much stronger that the still significant noise (which is gone when unbalancing/subtracting). > > The OP should consider to use microphone output instead and to use a > pre-amp for the input. There is a microphone output? I haven't used the microphone input as it provides a bit of voltage for a cheap microphone's amp, which is not required for mine, because it is battery-powered. > > I suspect to care about cable length and impedance is more important > than to fake a balanced input. Yeah, must be the cable length. It's always the cable length. > I doubt that a faked balanced input using > two unbalanced mono inputs of an elcheapo audio device is good for any > kind of measurement or audio recording. I agree with you on that - that is why I described my approach as experimental in the first place. > > Btw. there's always a discussion if the cold output should be > open-circuit for balanced output to unbalanced input. So you could > consider the unbalanced to unbalanced connections I posted as wrong. > OTOH a connection of cold and ground is wanted for unbalanced output to > balanced input. We could discuss the amount of cores of the cable, to > provide the latter, but since this thread is about balanced to faked > balanced, we could add a discussion about balanced to balanced > grounding. The grounding between balanced IOs could also be done in > different ways. > >> Note that he does not say what "measurements" he wants to do. If it is >> just levels then the crappy sound card might do, but even freq >> response is liable to be dominated by his the response of his sound >> card. And noise is almost certainly dominated by the sound card. > IIRC the OP even didn't mention if the microphone should be used for > measurements or underwater vocal recording. That's actually off topic to answer my question - if unbalancing (subtracting left and right) can be done by ALSA. As it seems to be important for you guys: I'm currently configuring DSP-based crossovers for active speakers, which involves measurements of the speakers' impulse and frequency response. > > We aren't talking about a professional solution, we are talking about > the advantage to fake a balanced input when using a crappy user input > device in combination with the balanced output of a measuring > microphone. > > There's no advantage! Wrong: At least, it cancels the noise of the sound card. Of course, that's evidence of the lost-cost hardware problem everybody keeps complaining about. And, as with every proper balanced connection, interference introduced to both the non-inverted and the inverted line at the same level is canceled when finally subtracting them. I don't see why that would not work. Matching levels and impedance is another issue. > We do not need to care about technical reasons > pro and con a faked balanced input by two unbalanced inputs. We simply > should notice that 1. relatively good balanced pre-amps are very cheap > nowadays and 2. they were more expensive years ago, when nobody > considered to make two unbalanced inputs of home recording gear a faked > balanced input. Why wasn't this done? Nobody was brilliant enough to > think about this superp idea? Do you have evidence anybody did think about it? It's not about having the brightest idea for me - I just wanted to know how to realize it, which I now do. And, in fact, I'm far more interested in technical reasons than in historical or economical ones, as the latter cannot prove that the idea was wrong. To my understanding, technical ones so far couldn't either. > > "Unbalanced stereo input as balanced mono input" is an utterly wrong > idea. That must be why it works. See? I can be sarcastic, too. Why is it so important to you that the idea was wrong? Sure, a better audio interface with a proper amp is preferrable. But if you only have the mic and a PC with a consumer sound card - why not to unbalance in software if that solution performs clearly better than just grounding the cold line? > > I recommend to get a cheap, but anyway relatively good microphone > pre-amp or directly pay for a better audio card with an integrated > microphone pre-amp and FWIW to use defaults regarding the grounding, > IOW not to modify gear and to use averaged, common cables. > > If getting new equipment shouldn't be an option, I would use the > provided IOs as they are and not fake a balanced input. I think you keep confusing two different questions: (1) Can it be done? (2) Should it be done? My question was (1), and Clemens helped to answer it. You're chewing on (2) like a bulldog on a bone. In order to calm things down a bit: I'm planning to acquire a better audio interface, probably an ESI Maya44 XTe or a Presonus AudioBox iOne. As I haven't decided yet if it's going to be internal (PCIe) or external (USB) and I'm not eventually sure about Linux compatibility, the fake-balanced input will currently have to do as a fill-in to develop a suitable measurement process. Regards Gunnar ------------------------------------------------------------------------------ _______________________________________________ Alsa-user mailing list Alsa-user@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-user
