Faber Acoustical Forum

Faber Acoustical Products for Mac => SignalScope => Topic started by: rdatman on September 18, 2007, 04:46:53 PM

Title: Problems with Audio input selection
Post by: rdatman on September 18, 2007, 04:46:53 PM
Is there a known issue with the selection of the audio input source.  It appears that the signal is always registering something from the internal microphones even when selected to input the external source.  I have tried to do this both from the system sound control panel as well as the program module both simultaneously or separately.  
E
Title: Re: Problems with Audio input selection
Post by: FaberAST on September 19, 2007, 09:05:01 AM
Eugene,

There is no known problem with audio input selection in SignalScope. What external source are you trying to select?
Title: Re: Problems with Audio input selection
Post by: rdatman on October 01, 2007, 08:37:54 AM
Eugene,

There is no known problem with audio input selection in SignalScope. What external source are you trying to select?


I am selecting input from internal to line in.  When line in is selected it seems that there is a ghost signal from the internals bleeding through. 

Another anomaly that is present is that the program seems to drop the input voltage 5 db or so on one of the inputs when using the unit in stereo for microphone pairing purposes.  (the red plot is 5 db hotter than the green) but only when the input is selected as line in.  Weird.

Eugene
Title: Re: Problems with Audio input selection
Post by: FaberAST on October 01, 2007, 10:50:56 AM
In order to help troubleshoot the problem, it would help to know exactly what model of Mac you are using, which version of OS X is running, and exactly what hardware you have connected to the line input (and how it is connected).

Ben
Title: Re: Problems with Audio input selection
Post by: rdatman on October 01, 2007, 04:05:50 PM
I am running a G4 Powerbook 1.5GHz PPC, OSX 10.4.10

A couple of questions, I take it the powerbook only has a mono built in mic?  I ask because the scope acts like it has two discrete inputs when set to internal.  Also should I make any effort to change the input under the system control panel for sound?  or just through the program, like I have been doing. 

What I am using the program for is to read the commonalities in the relative sensitivity of microphones to group them into stereo pairs.  I set the scope to "both, FFT analyzer,  22050, 1054, Db autoscale, log, uniform,exponential, 10"  Under input I have "built in audio, line in, 44100,  stream one (pulldown inoperative), and 24 bit"

I hope that helps.

Eugene


Title: Re: Problems with Audio input selection
Post by: FaberAST on October 05, 2007, 09:24:22 AM
Quote
I take it the powerbook only has a mono built in mic?  I ask because the scope acts like it has two discrete inputs when set to internal.

Typically, the built-in mic gets routed to both channels of input.  From SignalScope's perspective, then, the built-in audio device appears to have 2 discrete channels when the built-in mic is selected, but the signals are the same.

Quote
Also should I make any effort to change the input under the system control panel for sound?  or just through the program

You should just make the change within SignalScope.

Quote
(the red plot is 5 db hotter than the green) but only when the input is selected as line in.

Is this when you have two mics connected to the line input?  It's possible that one microphone is more sensitive than the other.  It's also possible that this is a result of the way the mics are physically connected to the input.  Another possibility, which seems very unlikely, is that there is actually a problem with the built-in audio codec in your Powerbook.

Ben

Title: Re: Problems with Audio input selection
Post by: rdatman on October 16, 2007, 09:11:05 AM
Sorry it's taken me so long to get back to you.

No. I am certain that the microphones are not the issue.  Because I have checked these against each other numerous times in Protools and an actually checking their sensitivity using this scope program.

It sounds to me like there are two options, one, the powerbook is defective.

Two, the software has a glitch, you are unaware of. 

i need to find a way of accurately measuring the inputs using another application to check out the first issue.
Title: Re: Problems with Audio input selection
Post by: FaberAST on October 19, 2007, 11:49:32 AM
What type of microphones are you using?  Dynamic?  Condenser?
What type of connectors do the mics have?  XLR?  1/4" phone plug?  Mini plug?
Do they require preamps?  Phantom Power?
Are they routed through any kind of mixer (or other hardware) before being routed into your PowerBook?

You mentioned that you have worked with Pro Tools, which suggests that you have access to a compatible audio interface.  Have you tried using that to get your mic signals into SignalScope, instead of using the built-in input?

Depending on what type of mics you have, there can be various places along the signal chain for problems to arise.  This is why I asked before about your exact setup.

Ben
Title: Re: Problems with Audio input selection
Post by: rdatman on October 29, 2007, 06:10:58 PM
I have elimintaed the variability of output by confirming that the left and right channels going into the computer are completely equal in output at a given input.  (Certainly a .3-.5 db variability is not accounting for 3-5 db at the faber accoustic interface.)  what I need to know is that is there any way that the software could be misreading one of the two inputs by 3-5 db, not what is causing it if it's not caused by your software.

I dont know how much testing the software gets after it is designed, and how often specific models of powerbooks have anolmalies that might could bring about such an event.

E

Neumann KM184 mics (XLR) were used and a prootools 002rack interface unbalanced out stereo mini to rca adapter
Title: Re: Problems with Audio input selection
Post by: FaberAST on October 30, 2007, 12:58:09 PM
I don't believe that either SignalScope or your line input is causing this particular problem--both are highly unlikely.

Here's another possibility:  Open the Audio MIDI Setup application (found in /Applications/Utilities) and, under the Audio Devices tab, look at the properties for the Line In source of your built-in audio device.  You will see a Volume slider for each input channel.  Do they have the same value?  If not, that is almost certainly the reason for the discrepancy in SignalScope.

Ben