Find PC's Audio Out Voltage without CRO

Pead the datashees for the parts involved and compute from there....

What's a CRO? Oh, a Cathode Ray Oscilloscope. Got it.

There is plenty of sound card control software available for the PC that includes an output indicator. The problem is that the indication is usually a guess based on the sound card amplifier gain. So, you get to calibrate the readings in order to get an accurate output. There is also oscilloscope emulation software such as: but that only shows the level of the audio input, not the output.

Perhaps a PC VU meter. Lots to choose from: all of which again give the audio input or mixer levels, not the output level.

I'm out of ideas. Since there's nothing on a sound card that connects to the audio output jack, what can be used as an input to measure something, methinks it can't be done unless you either use one channel to measure the level on the other channel, or you add a 2nd sound card or USB sound dongle.

The 2nd sound card is not that horrible a solution. Let's say you're using an internal PCI or motherboard sound card for driving the headphone. Add a USB sound dongle to the machine. Install a 3.5mm earphone jack "tee" connector into the internal sound card output port. Run a cable from one port of the "tee" to the input of the USB sound dongle. The other port goes to the earphone. Install and run any of the vu meter programs and have it monitor the USB sound dongle. Now, you're monitoring the sound output instead of the input or mixer. Of course, you'll need to calibrate this thing, but you only do that once. Umm... look into software that saves your sound card settings as many programs like to change those settings.

I have the feeling that this isn't exactly what you want. Perhaps it would be helpful if you disclose more about what you're trying to accomplish?

It's for a rather delicate stereo front end, and to prevent overdriving, without having to hook up external test gear in each instance.

I think the closest I will get is playing the track through an audio editing application, like Audacity, and calibrating the VU meters.

Obviously, such programs can read the output voltage. Would seem easy enough to write a app that could provide a numeric readout.

Bob Griffin

Oscilloscope software + 2nd soundcard, as John said. Might not be very useful for the averag user though.

make it less delicate? Use ears to detect overdrive?

Reporting voltage is not one of a soundcard's functions afaik. If they read dc you could caibrate near enough with a new battery, but they're ac only.

NT

Ok. However, I don't think using software at the source is a good idea. If the stereo "front end" is that delicate, you might blow it up just by turning on the PC and producing a glitch. Or, some other program might decide that it controls the sound card, changes all the settings, and blows up your "frond end".

Instead, I suggest an external hardware solution. Not a meter, but rather a limiter of some sorts. I believe those can purchased, but I'm not familiar with what's available.

Nope. None of the PC applications are reading the output voltage. They look at the mixer voltage and measure that. See: and look at the block diagram: The PC software only has access to D/A chip. The A/D is for recording and is not used for measuring signal levels. It could be, as I described where you use one channel to measure the output of another channel, but it's usually not done that way.

The PC knows what is going into the D/A converter and uses that information to determine the output level. If you could back feed the low level audio output jack on the sound card with some audio, it would not show up on any software VU meter program. Only audio data that goes into the D/A can be displayed.

From there, the audio goes to the "line" jack and also to the speaker output. The gain between the mixer and the "line" jack is known (I think it's x1) and fixed. The mixer gain is also known and fixed (also x1). With those numbers the "line" output level can be calculated from the D/A levels.

If you look at typical audio control, music, whatever audio software, you never see a bar graph or meter showing the speaker output level. That's because the speaker audio amplifier gain is purely analog and of an unknown gain. Therefore, its output level cannot be calculated from D/A levels and the subsequent gains. Note that the mixer is also purely analog and has the same problem.

Therefore, the only numbers you can get directly for a playback VU meter come from the D/A converter on the sound card. They don't measure anything (in playback) because there are no A/D converters present (except for the audio input A/D which is not used in playback).

Got it?

if all you want is input protection, put two signal diodes or ones with low CAP in seriels back to back across the input of the stereo. Most line inputs are ~ 0.650V rated, 1V Peak. The diodes will give you just over that for clamping..

Also, you could use the center ties of the diodes to drive a Hi-Z LED circuit for overdrive indication.

Put them in antiparallel. It won't work otherwise.

Now they will. For lower voltage use schottkies.

NT

You might want to reword that so someone who doesn't already know what you think you mean can figger it out.

While protection is good, that method will make the audiophools heads explode thinking about nonlinearity.

well I had a zener seriess limiter circuit in mind when I wrote that..

Its obvious not going to work here, since I doubt we can get zeners under a 1 volt, but I could be wrong there. anyway..

Two sets of series diodes back to front will give a compression of ~ 1.4 volts or so..

of course two diodes back to front in parellel can offer some lower clamping protection being close to the threshold of the input level.

As for the indicator using the double sets, you can tap from one of the centers as a reference to a LED over drive circuit.

If pictures tells the story better I can supply that, too.

To each his own I guess.

Yes, from the responses so far, this appears to be the case.

However, this pertaining to Visual Analyzer might be relevant.

Bob Griffin

a high efficiency red LED, or two antiparallel might be a good start.

Do you mean AC amplitude (averaged over many cycles), or do you intend to record a peak value?

Either way, there's a large variety of measurement options. At the crude end, use a power amplifier and a waterproofed resistor, and see how long it takes to boil away some water... Then, your problem becomes that of relating 'half a liter boiled away in seventeen minutes' to the level you wish to achieve.

For good reasons, most people use a meter.

Maybe this might work

But as stated here and on this website, you can feedback the output to the linein to measure it.

Cheers

No meter.. you mean I can't use a DMM?