One of the first questions that comes to our mind when we hear the term ‘audio interface’ is whether or not they really are necessary. The simple answer to this question would be no, as there are audio interfaces that do not require any output devices. These types of interfaces have been created in order to avoid or null out any potential digital audio interface function and, thus, they are a waste of money for those who need them but cannot afford them. However, even if they are not needed, their presence may still have some advantages as they may make the process of connecting different peripherals easier.
In general audio interface output is a ground/surface waveform with a certain frequency range. The signal that has been applied to the analog audio interface device will either have been compressed (or compressed to some extent) in order to reduce noises, or it will have been ‘pumped’ using a bi-conductor circuit or potentiometer into a low impedance output device.
The output from the analog audio interface will then be subjected to one or more filters in order to remove any excess noise that may have been derived during the generation of the signal. The filters used here act on the signal in such a way that they attempt to remove undesirable high frequency components. This process is known as clipping, and although it can eliminate some very high frequency sounds, it also leaves all other frequencies unaltered.
An example of the clipping stage of an analog audio interface device would be the headphone that you connect to your computer using a USB cable or through a FireWire port. You will hear a high frequency sound effect as your headphone is trying to eliminate some excess noise, which in turn is also trying to eliminate some high frequency vibrations that originated from the input signal. It should be noted that even though such outputs are called ‘pre-ampifiers’ they are not actually required for connecting audio peripherals to your computer. If you already have a sound card and a headphone that work with it, then an audio card may not be required at all, as it will not be able to use any pre-amps.
As aforementioned, most signals that come through an analog audio interface will travel through several stages along the way before reaching their final destination. The first stage that the signal goes through is the demodulation stage. This is usually accomplished using a lower frequency noise gate, although sometimes a bandpass filter will also be employed.
The demodulation stage then transforms the signal to a lower level in order to prevent it from being spiked (or canceled) by external influences. The final conversion process here uses a high frequency oscillator in order to convert the high wave of the signal back to a lower level. Once this is done, the converted signal will then be amplified using a power transistor.
The final stage of the conversion process, which is the measurement of the resulting audio level is known as the clipping stage. The purpose of the clipping point is to ensure that no unwanted high or low level audio is left in the signal. On some devices, such as some MP3 players, there is a facility that allows the playback of the signal after it has been clipped. This will result in an audible ‘clipping’ of the audio, but the quality of the audio will not be very good as the clipping point has not been met. In this case, it is important to make sure that you do not try to listen to the clipping point (ignoring all other aspects of the signal).
Although most of these parts will not be essential to the operation of your AVR or computer program, they are nevertheless vital to the proper functioning of the device. In particular, if your AVR has a user-interface, then you will need to be sure that you can access all of its features from your audio interface. If you are not certain of this, then it may be worthwhile hiring an external input or output device to make things easier for you. You should be able to connect your input device to your computer easily and use all of its features.
