# The basics on digital audio interfaces



## bantam (Oct 25, 2009)

So here's a quick rundown of the basics in digital audio interfaces...

Let's say you are trying to record a source (guitar voice whatever). You need a MIC, that mic will need to be amplified by a preamp. Once the mics signal has been amplified by a preamp it can be plugged into an audio interface. These used to be called soundcards because they were cards plugged into pci slots on a motherboard. These days they are mostly usb and firewire. 

Audio interfaces usually have inputs that are either MIC level (meaning the mic preamp is built in-for pluggin xlr cables with mics attached) , line level (for plugging external mic preamps, synths, CD/tape players or outboard effects into), or DI -direct inject(a high impedance input that can accept guitars/basses and amplify them).

These inputs are connected internally to one or more channels of ADC (analog to digital converter) that will change your amplified mic signal into digital data that can be store on your computer. To playback what is recorded, interfaces also contain one or more channels of DAC (digital to analog converters) that allow you to press play on your computer and the digital information is converted back to analog so that you can hear it through the headphone jack or monitor outputs. Most pro-sumer/pro interfaces today sample audio signals at 24 bits per sample. CDs have a bit 'depth' of only 16bits per sample so audio software offers the ability to convert this bit depth down to 16bits prior to burning to CD.

The last important piece that interfaces have is a clock. This sets the rate at which the audio wave is sampled. CD audio has a sample rate of 44.1kHz. This is fine for rock pop IMHO. You may want to use higher sample rates (88.2kHz or 96kHz) for jazz or acoustic music but as with bit depth you have to covert this rate down to 44.1kHz prior to burning to CD.

There are many other features available on today's audio interfaces (midi, digital signal processing DSP, onboard mixing etc...) but non affects the sound quality of your final product like the ADC/DAC and clock. The better these are the better chance you have of getting it right at the source (during recording) and mixing without the negative effects of jitter (clock errors that can collapse the perceived stereo image and add a grainy-ness). (without talking about mic placement, room treatment, monitors....) 


For recommendations on interfaces check our reviews section!


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## ejbragg (Dec 13, 2009)

An interesting note about this subject is that you touched on everything of the highest importance in the area of classical music. Because orchestral music is so incredibly dynamic, there is a great need for the signal chain to be free of noise. Furthermore, the choral mics are often ribbon type, making the gain (without noise) difficult to achieve without adding color. So the microphones are extremely sensitive, the preamps are extremely sensitive (and still noiseless), and the output of the preamps goes straight to the A/D converters and to hard drive. No mixing boards at all in the signal path. This allows for the highest gain, lowest noise, most exact recording for this type of music.

Even in my studio now, I use this chain (with no mixer in-line with the DAW). I use mixers strictly for monitoring.

It seems as though one day, analog mixers might possibly become obsolete, once the digital software comes to a place where it can offer virtually limitless outputs without noticeable delay. It's a high order, but the industry is steadily approaching this capability.


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## bantam (Oct 25, 2009)

yes i want high fidelity clean converters. the color can come from the pres or other outboard if waranted but the color shouldn't come from the converters/clock. funny that now i have a very colored setup (neve/api) and im looking for a cleaner signal path so i have a way to go onto the drive in a pristine way and color to taste later.

i also didn't go into a discussion about the integrated mic pres because they may or may not be to your liking but as long as the adc/dac/clock is at a high fidelity level you can add other pres to the line inputs and still have a usefull interface.


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## fractile (Mar 15, 2009)

Eric brought up a profound concept I hadn't considered: recording direct without going through a mixer. Recording is all about getting the best possible signal recorded from each mic; mixing and mastering, etc. can come later.

So you could just as well use the mix board for just monitoring all the channels... eliminating another potential source of coloration/distortion during recording.


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