Recording Audio from a Computer

Recording Audio from a Computer

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Recording Audio from a Computer

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In this post, we turned to Shure Associate Gabe Benitez for an overview of computer recording considerations and fundamentals.

It wasn't that long ago - maybe 15 or 20 years at most –when a quality studio incorporating all of the technologies that have revolutionized recorded music over the decades would have cost tens of thousands of dollars. But now, anyone can produce a good quality recording on a simple home computer with a few hundred dollars worth of software. Better still, the Internet has provided a free channel for global music distribution – an opportunity well beyond the reach of the singer-songwriter or garage ban of yesteryear.

"…the computer music market went from just under $140 million in sales in 1999 to almost a half-billion dollars in 2008."

Consider this: According to the Los Angeles Times, over half the commercial recording studios in the L.A. area had closed or been sold to artists for private use. And NAMM, the trade association for music manufacturers, reported that the computer music market went from just under $140 million in sales in 1999 to almost a half-billion dollars in 2008.  Recording software like Avid Technology Inc.'s Pro Tools, Steinberg Media Technologies' Cubase and Apple Inc.'s Garage Band perform many of the tasks of old-school studio consoles and tape recorders at a fraction of the price.

Carr puts it this way: "Some people call it the triumph of the amateurs -- the ultimate democratization of the means of production. Others say it's the end of pop music as we know it."

Most Shure customers agree with the former and not the latter.  That's why "How do I connect a microphone to a sound card?" has held a top ten position question among 3,658 questions in's Technical FAQ (Find an Answer) section since 2002.

In this post, we turned to Shure Associate Gabe Benitez for an overview of the basics.   First, we'll cover some fundamental concepts.  Then, we'll move on to considerations when using an XLR-to-USB adapter.

Fundamental Considerations for Computer Recording

The growing popularity of home studio recording consistently raises the question of interfacing professional microphones with computer sound cards. Unfortunately, sound cards are rarely designed for professional microphone use. They often provide poor, low level and noisy sound that doesn't match the quality of the recording package or the mic.  The good news is that properly interfacing a mic to a sound card isn't that difficult.

In order to interface a microphone to any device, we have to consider the electrical and mechanical compatibility between them. Here's what that means:

1. Signal level

This is the actual voltage that comes out of a source or is needed by a receiving device, for example a sound card. Professional microphones put out a very low voltage in the range of 1 millivolt (1/1000th of a volt). Sound cards on the other hand require levels in the order of 10 millivolts (ten times as much!). So the first step is to increase the level before we get to the sound card.

2. Impedance

This is similar to resistance and its vital when interfacing two circuits. The relationship between the source impedance (microphone) and the load impedance (sound card) will determine how much of the energy coming from the mic is actually transferred to the sound card. Load impedance should be around ten times the source impedance. Professional microphones usually have between 150-600 Ohms. Soundcards have between 600-2000 Ohms. In most cases impedance will not be problematic.

3. Connector and wiring scheme

This is probably the most visible of the problems. There are more than a few connector types in the audio industry. Professional microphones use XLR connectors. Sound cards, due to space constraints, are equipped with a smaller connector, usually a 3.5mm "miniplug". Although these look the same from the outside, there are at least three different types and multiple wiring schemes. Unfortunately, there is no standard for sound cards. Some are balanced, others are stereo, and others provide bias in separate wires. On most sound cards there is a line input next to the mic input that has the same connector. The line input is far more standardized than the mic input. This, as it will be explained later, will let us properly connect a microphone to the sound card.

4. Dynamic vs. Condenser

Connecting a condenser mic to a sound card requires power, while a dynamic does not. Although sound cards can provide bias, they will not provide or have the capability to supply the phantom power that is needed for condenser mics. If you want to use a studio-grade condenser microphone, you will need an external power supply.

This may all seem a little daunting, but there's a simple way to connect just about any microphone to a sound card and that's by using an external microphone preamplifier that has a line and/or a USB output. If you use the line output, connect it to the line input of the sound card. If the preamplifier has a USB output, even better – avoid the sound card and go directly to the computer through the USB port. These preamplifiers come in different shapes, forms and prices (with some as low as $40) and many will let you connect a dynamic or condenser microphone (if they provide phantom power) and gives you the ability to get the professional sound that you would expect from your Shure microphone.

5. XLR-to-USB Adapter

No Sound Card Required
Shure introduced the X2u XLR-to-USB adapter in 2009. You already know about interfacing a professional wired microphone to a computer sound card (by reading the section above). But now, let's think about external digital devices that allow you to bypass the computer sound card altogether.

XLR & USB Connector Can Help Record Audio from a Computer

Remember that signal level is the actual voltage that comes out of a source. In some cases a microphone's output signal may be too low and must be increased before it connects to a sound card. If the increased signal is too high, distortion may result. If the signal isn't increased enough, it can quickly become noisy.

Here's what an adapter like the X2u does to solve this problem: The Shure X2u allows the gain to be changed before the analog to digital conversion. There is a signal LED to indicate proper signal level and distortion. Using the LED allows the user to avoid both distortion and noise optimizing the microphone signal for recording.

Computer sound cards have impedances and connection schemes that adapt to many consumer microphones. Professional microphones have impedances and connections schemes that are designed to interface with professional microphone mixers.

The X2u has a standard, pin 2 hot, female XLR connector and it also has an input impedance designed to work with many types of professional microphones. These built-in plug-and-play features make devices like the X2u easy to use.

X2U product shot

The X2u provides +48V of phantom power which feeds any modern and even some vintage condenser microphones. The Shure X2u uses your computer's USB for power. It's a good idea to turn off phantom power when using a dynamic microphone to extend it the life of your laptop battery.

The X2u is designed to substitute your computer sound card by providing an external professional microphone input and a headphone output. The headphone output is connected directly to the microphone input.  That's how zero latency monitoring is achieved. Use the headphone output to monitor both the signal recorded and the signal played back from the computer.

Easy and Budget-Friendly

Constructing a well-equipped recording studio twenty years ago ran into the millions of dollars.   Today, you can start small and still be professional with a computer, recording software (ProTools 10 for Students runs for about $300) and bundles like the SM58/X2u XLR-to-USB adapter, available just about anywhere for less than $200.