Computer audio - DI vs adapter

[unc417]

I used to connect my computer audio with a typical radioshack adapter to get 1/8 to xlr, now I have the Radial ProAV1 but notice no difference in audio quality. I guess the laptop is the weak link here, not sending very good audio quality.

I know that a DI is the proper way to do this, but my question is, whether it's a computer or ipod or whatever else, how can I justify the cost of a ProAV1 when a simple adapter will work? What is the real difference here and what are the risks of using the adapter?

Thanks

[[Admin] osborn4]

If you don't get a hum, then you should be able to use an adapter.

[Brad Weber]

Originally Posted by unc417

I used to connect my computer audio with a typical radioshack adapter to get 1/8 to xlr, now I have the Radial ProAV1 but notice no difference in audio quality. I guess the laptop is the weak link here, not sending very good audio quality.

I know that a DI is the proper way to do this, but my question is, whether it's a computer or ipod or whatever else, how can I justify the cost of a ProAV1 when a simple adapter will work? What is the real difference here and what are the risks of using the adapter?

A DI gives you a balanced, microphone level output and in the case of a transformer based DI like the AV1, provides transformer isolation. If the computer is right next to the mixer, you have line inputs available and there are no ground loop issues then the adapter may work fine. If the computer were at the front of the room some distance from the mixer, the computer would likely be powered off a different circuit than the mixer and you wanted to use existing microphone inputs, a DI would be a better choice and could avoid multiple potential problems.

Also, the AV1 incorporates an internal resistive summing circuit so the stereo computer input is mixed to a single mono output. You can't do that with a stereo 1/8" TRS to XLR adapter as tying left and right out of a computer together is usually a bad idea, so it would require either stereo 1/8" to two XLR connectors for two channels or using just one channel out of the computer.

[Frank DeWitt]

A di box is first a impedance matching device. It takes a line level high impedance signal and converts it to a microphone level low impedance signal. Second, it converts a unbalanced signal to a balanced signal. Third, because it uses a transformer, it is a very good tool for braking ground loops.

If your laptop is near your mixer, and you use a cable that takes the stereo output on the 1/8 in stereo jack and splits it to two 1/4 in plugs, or two RCA plugs and plug them into the line input of your mixer, and you don't have hum or other noises you are all set. There is no reason to use a DI box and a DI won't make it sound better.

If you have hum buzz, or other odd power supply noises, or if you are a long way from the mixer then a DI on one channel, or a resistive summing cable to a DI, or a DI with summing built in, or two DI boxes will help.

If you use a DI box then what matters is the transformer inside. All the buttons and switches are fluff, and in my opinion they can cause more trouble then they solve. (They are controls down on the platform where the musicians can reach them and you can't.)

Disclaimer, I make and sell DI boxes.

Frank

[Tim Padrick]

If you use a simple adapter (as opposed to say a 1/8" TRS to dual 1/4" TS cable) then you are either getting only one channel of the computer, or you are getting the sum of the two channels with one of them polarity reversed - which means you will get only those signals that are not panned to center, the strength being directly proportional to how far off center the signal is panned.

With modern equipment, "impedance matching" is often irrelevant - see http://www.padrick.net/LiveSound/Interfacing.htm