usb audio interface

[cjbrooks91671]

Sorry in advance if this question has already been answered. How does a USB audio interface work (like for example the tascam US-144)? Is the PC's soundcard still doing the recording? Or is the audio signal somehow "pre-saved" in a digital format (such as *.wav) before it even gets to the hard drive?

I was thinking of getting one of these - my soundcard has RCA-type digital I/O (which works awesome with Vegas 6 for recording perfect quality drumtracks from the Roland TD-20 perc. sound module, which has digital out). If I have a usb interface for guitars/vocals, would I then use digital out (like on the tascam US-144), and record with the soundcard? Or is recording with a usb interface totally different?

Thx much.

[scottdemarko]

Briefly the answers to your questions are no the external audio interface will be taking the place of your sound card when selected. No the audio is not pre-saved.... Read on to for more detail...


What is an audio interface?
In simplest terms, an audio interface connects your microphones and other sound sources to your computer - it bridges the gap from analog to digital. Audio interfaces are commonly equipped with mic preamps, line inputs, and a variety of other input options.

You might be asking yourself, "If audio interfaces are often equipped with preamps, why wouldn't I just buy a channel strip or preamp?" Well, the answer to that question lies in the analog-to-digital conversion. Traditional preamps and channel strips send out an analog signal, and for audio to be usable by a computer, it needs to be digital. The audio interface converts the analog signal from its inputs to a digital output, making it easily digestible for a computer.


Why isn't my computer's built-in sound card sufficient?
If you're serious about recording audio, you'll quickly become dissatisfied with your computer's limited audio capabilities. Most consumer sound cards aren't equipped with high-quality analog/digital converters to adequately make the transition from the analog world to digital. They're fine for gaming or listening to MP3s, but consumer sound cards lack the headroom and the power to preserve the signal integrity. It is important to note that poor A/D conversion is largely what led to early forays into digital recording to be regarded as "harsh."

Another drawback of consumer cards is that most of them only support two channels of simultaneous audio, making it nearly impossible to track drum kits or entire bands without a LOT of submixing and creative bussing. Aside from the poor-quality conversion, consumer cards are prone to excessive latency, jitter (errors in timing that "smear" the audio signal), and overall inferior sound quality.



Inputs and Outputs
With the exception of computer connectivity, no other feature set plays as big a role in choosing an interface as the number of, and type of inputs and outputs. From the 2-channel PreSonus Firebox to the 12-channel Mackie Onyx 1200F, there are audio interfaces to meet almost any I/O need. If miking a full drum kit with close mics everywhere, an interface with eight inputs would be a good choice. Conversely, if your only intentions are to record your voice and an acoustic guitar, two inputs will do nicely.


Manufacturers have recognized the need for specialized interfaces for the different types of performers and introduced application-specific devices for guitarists and keyboard players. Line 6's TonePort series include both mic preamps and hi-Z guitar inputs, and also offer emulations of amps, guitars, effects, and vintage studio gear, perfect for axe-slingers with recording aspirations. On the keyboard side of things, M-Audio's Ozone MIDI controller/audio interface provides a mic pre along with a 25-key MIDI controller.

Many interfaces have the ability to output a digital signal. This digital connection usually comes in the form of S/PDIF or ADAT lightpipe formats. Digital inputs are cool since digital signals obviously don't need conversion. Plus, ADAT lightpipe is capable of carrying eight channels of up to 48kHz audio via a single cable, which can be a very handy tool for upping the number of simultaneous inputs.

Of course, it does no good to record your masterpiece as great-sounding digital audio if you can't hear the playback. A viable audio interface should have monitor outputs for the connection of a set of studio monitors. These can take the form of digital or analog outputs. And while we're talking about outputs, many current interfaces have at least a few outputs for sending audio from the interface to external processing devices, and back again.

Do bit depth and sample rate matter?

Yes and yes. Next question. Seriously though, bit depth and sample rate are very important considerations when it comes to choosing an audio interface. The number of bits determines the theoretical maximum dynamic range of the audio data regardless of sample rate. Each additional bit adds 6dB to the dynamic range of the audio. More bits help capture quieter signals more accurately. On the sample rate side of things, think of it as snapshots. At 44.1kHz, the computer is taking 44,100 "pictures" of the audio every second as it enters the computer. Obviously, the higher the sample rate, the more "pictures" get taken, resulting in a more accurate representation of the original audio.

If your only expectation is to produce demo-quality CDs to hand out to friends and family, or maybe sell at a local show, 16-bit/44.1 kHz (commonly known as "CD quality") will be fine. Conversely, if your objective is to record string quartets, an audio interface that is capable of doing 24-bit/96kHz or even 192kHz is desirable. With DVD video and audio capable of utilizing 24-bit/96kHz audio, today's market is full of devices capable of reproducing high-resolution audio. Ask any group of engineers and you'll get many different answers concerning bit depth and sample rate, but keep in mind that the bit depth provides more headroom when recording, so greater bit depth is more desirable than high sample rate when it comes to basic music recording. Plus, stepping up to a higher sample-rate sometimes comes as a trade-off, reducing track count.

This article was pulled from Sweetwater's buying guide on purchasing an audio interface... Check out http://www.sweetwater.com/shop/computer-audio/audio_interfaces/buying_guide.php for more info on audio interfaces and computer recording.

[FoxeFire]

Hi,
I have an emachine T1110 80 gig hard drive
Intel Celeron
1.00 GHz 256 MB RAM
Windows XP service pack 2
I'm a singer songwriter and at the most will probably need 4 inputs
2 guitars two vocals at the same time.
What are my options for a usb audio interface? What kind of luck have you had with them?
How well do they interface with Sonar Cakewalk?
Thank you,
Blessings and Balance,
Ernest