Does input equal output?

[mitch57]

My co-worker and I are having a discussion on how sound works. Neither of us is very knowledgeable when it comes to audio and video. Sorry for the long post but I don't know how else to describe the debate. This post has to do with amplification so I am putting it here.

Here's the situation. We have some PCs that have Sound Cards built into the chipset on the motherboard. The volume is so low that in order to hear anything we need to either use powered headphones or powered desktop speakers.

As a test we installed a seperate PCI sound card to see if we would see an improvement in volume without using powered headphones or speakers. We experienced a significant volume increase with the PCI sound card.

Here's where the debate comes into play.

If you put an amplifier with the same specifications between each of the sound cards and headphones/speakers will the outup volume be the same on both sound cards or will the PCI card volume be higher then the built in sound card? The amplifer used for this test is a cheap mini jack rca amplifer (radio shack) that runs off of two AA batteries and has a slider volume control.

We hooked up the amplifier to the PC with the built in sound card and the volume is definitely louder. We haven't tested it with the PCI sound card to see if it is louder then the built in sound card with all other things being equal.

In theory what should the end result be? Should both sound cards have equal output volume or will the PCI sound card be louder (assuming the radio shack amplifier is set to the same volume setting)?

 

[MDS]

What you are noticing is the difference in the line-level output voltage between the motherboard down sound chip and the separate PCI card. If the input to the amplifier is higher, then the amp will produce a louder output compared to using the soundcard that feeds it a lower voltage (up to a point).

An easy example to clarify would be the output from a tv's audio outs connected to an amplifier. If you set it to 'fixed', the output voltage is typcially 150 mv. If you set it to 'variable', it typically ranges from 0-250mv (using my Toshiba as an example). So if the tv volume were all the way up, using the variable out would produce a slightly higher volume level for a given setting on the amp.

The same thing applies to line level ("pre-out") outputs from a pre-amp, although they are fairly standard and are usually around 1V.

 

[BMXTRIX]

There are usually two outputs from sound cards and they should be at different levels.

1. The headphone output: This output should have enough power on it to run a set of headphones without the headphones needing additional power. On your PC there is usually a headphone jack in front to plug into and likely taps into the internal sound card. The PCI card probably has a headphone jack in the back. It may pull a little more power off the system and allow for greater volume than the one using the built in sound card.

2. The other output is going to be your line level output for external speakers. Line level from either card should be identical and it most DEFINITELY requires amplification. All computer speakers on the face of the earth use some sort of amplifier. If you don't have an amplifier, it would be like connecting a speaker directly to the output of your DVD player and wondering why you couldn't hear anything. The answer is that there is no amplificaiton behind a line level output from your PC, or a DVD player, cable box, VCR, etc. First it must go through some sort of amplifier, then to speakers. Line level audio has a standard voltage associated with it (which I don't have memorized) which all audio components should follow (but don't).

 

[mitch57]

BMXTRIX,

"The answer is that there is no amplificaiton behind a line level output from your PC, or a DVD player, cable box, VCR, etc. First it must go through some sort of amplifier, then to speakers. Line level audio has a standard voltage associated with it (which I don't have memorized) which all audio components should follow (but don't)."

In my case the line level output appears to be differnet. Based on that should the PCI sound card be louder?

By the way, we connected to the headphones to the headphone jack on both sound cards and the results are still the same. You can barely hear anything out of the sound card on the motherboard but the one on the PCI sound card is acceptable.

I guess I still don't get it.

My co-workers theory is if the signal leaving the sound card is higher going into the amplifier then the signal leaving the amplifier will be louder as well. He claims that if we connect the radio shack amplifer to the line out on the PCI sound card it will be louder then the built in sound card when the amplifier is set to the same volume level.

 

[MDS]

Line level audio has a standard voltage associated with it (which I don't have memorized) which all audio components should follow (but don't).

That's the point I was making in the first reply. There are no standards for line level out for sound cards. I did assume the amp was connected using line level out as it doesn't make much sense to use the headphone out.

My co-workers theory is if the signal leaving the sound card is higher going into the amplifier then the signal leaving the amplifier will be louder as well. He claims that if we connect the radio shack amplifer to the line out on the PCI sound card it will be louder then the built in sound card when the amplifier is set to the same volume level

Your co-worker's theory is correct.