Controlling the Soundcard Input


    It is important to get a good signal from your soundcard, with the minimum of electronic noise. A VU meter can be shown to give a sense of the signal strength while you view the tuning graph. This will be visible on the right edge of the window, but you can position it instead at the top (or you can hide it, but it is generally useful to display). A good signal should show more than half the height at the loudest volume.

    Tuning Meister has a simple oscilloscope function begun under Options | Waveform Graph. This is useful for determining the quality of your soundcard's signal. So if you can't get a proper tuning trace this mode might help you discover certain problems. You can see whatever noise might be lurking when there is no input signal, such as a 60-cycle hum or little blips from other electronic interference. You might also check strong signals for clipping (discussed in detail below). While this is often indicated in the VU meter with a red flag, some sound cards create clipping situations without going full scale; in this situation Tuning Meister will not detect the clipping and no red flag will show. Even more disastrously, some sound cards invert signals that go beyond full scale, and that will create major problems with the tuning analysis. A good signal might look like this on the 'scope function.


strong signal


 A poor signal means the tuning function will struggle to decide on the pitch; and the tuning trace will be very unfocused, broad and wiggly.
    You can "Pause" [press keyboard "P" most easily] the display, just as with the tuning trace, if you want the scope trace to freeze. [Resume with any other keypress].

  Windows provides a Recording Control, similar to the Volume Control which can be launched by double-clicking on the speaker icon in the System Tray. However, the path to this control is well-hidden (indeed, I had to call tech support to find it, when I moved to W95 from the old W3.1). So to make it easy, the Recording Control can be launched from Tuning Meister at Soundcard | Input Volume Control.
   
    This Control is what you use to select which physical lines coming into the soundcard are to be read by the computer. These lines might include a microphone, a Line-In cable (this is a signal that is amplified, such as from a microphone pre-amp, or the output from your stereo), and lines hidden inside the computer such as the output from the computer's CD player. So if you are not getting the desired signal into Tuning Meister (nothing shows up in its VU meter) then probably you need to select something different in the Recording Control. For instance, you might wish to analyze some CD performance. You will have to be sure that CD Player is selected, or more commonly today, Stereo Mix (see further discussion below). You have to keep an eye on the settings; sometimes they get changed by another program, without your realizing it. For instance, when you launch Skype it automatically (quite sensibly) selects the microphone as input; if you were using Stereo Mix and returned to TuningMeister expecting Stereo Mix you would have trouble, which might not be immediately obvious since the microphone might pick up the speaker out. So TuningMeister would tune, but it would probably not give a strong result. Just keep these hidden stumbling blocks in mind.
In the Recording Control you will also adjust the input volume so that it is strong but not clipping (this means, that the signal is too strong for the range of the soundcard, and the waveform displays a flat top and/or bottom, as below).


clipping image


A slight amount of clipping as below will not affect the tuning accuracy, but will definitely cause distortion in a recorded performance.


slight clipping


     Note that microphone inputs are almost all monophonic, so if you want a stereo signal, it must come from Line-In.
    Unfortunately, many new computers, especially laptops, save a few pennies by not including a separate Line-In input. They may show Line-In in the Recording Control, but it is mostly a fake. It's a sad situation. There then will be no way to input an outside stereo signal into the computer, without investing in an external sound card. (Many devices are available that connect, primarily with a USB plug).

    The Recording and Volume controls reflect the particular design of the mixer functions supplied with the soundcard, and they vary somewhat from one computer to the next. Windows has no standard format for them. The two main differences I have found are that some mixers allow you to select only one input line at a time, through a box labeled "Select",

Recording Control with Select


    while other mixers are set up to allow multiple inputs; ones you don't want are stopped by checking their corresponding "Mute" box.


Mute boxes


    If you haven't used the Recording Control before, it may not display all the mixer lines that are available that you want to use. In that case, from Options | Properties within the Recording Control you will encounter a dialog listing all the available controls. Check all the ones you wish shown. Some may not be of interest such as telephone input and you can hide them for less clutter.

    Some mixers offer a control which adjusts the overall input volume (in the lower image, the left-hand control), in addition to the separate volume controls for each particular line. Perhaps it would have been better to call it Master Recording or something like that.

    In the controls for the Santa Cruz soundcard, it might seem as if the possibility of mixing inputs doesn't exist at all. But the selected control, Stereo Mix, actually means the mix of all the inputs but doesn't seem to give any way to control the constituents of the mix itself.  In this case the soundcard comes with its own mixer applet, which contains that functionality. So if your soundcard has its own special mixer program, that instead of the Windows generic mixer should be your primary way of controlling input. That mixer you will have to launch directly yourself; TuningMeister won't know about it. And under some operating systems this link to the mixer does not seem to work - again, you are on your own.


    With 16-bit data, the usual mode of operation, [not many soundcards are less than that these days], the oscilloscope has an automatic gain increase with quiet signals, which it indicates by drawing the expanded signal in various colors. You will see several forms superimposed at different magnifications. So as the most sensitive trace, red, gets bigger, it gives way to a green, then a blue trace, and finally black. [Illustrated below]. That way you can see the shape more easily. Simultaneously, the regular trace continues in black. The red trace has 256 times the sensitivity of the black trace. If I just showed the black trace, you could not see that was some noise in the signal, affecting quiet input.

    Note the noise in this image of my laptop's microphone input at rest, much more obvious in the magnified [red] trace, which comes from some electronic interference affecting the sound card. You can not always get rid of that noise, but a stronger signal will lessen its effect on the pitch calculations.

low signal

        The noise has almost completely disappeared when I plug a (cheap Radio Shack) external microphone into the computer. [You might not be so lucky].

with external microphone

    Now with a soft tone sung into the microphone.

scope - soft input

    As the tone gets louder, it moves beyond the scale that the red trace can handle, so that disappears.

scope moderate input

    Louder still and the green trace disappears.

scope still more input

    Finally, only the black trace remains. If it gets somewhat louder than this, clipping will be seen.

scope strong input

I hope that this flexible changing scale is easily understood.

 

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