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Understanding the signal flow of audio and MIDI data, and the gain stages along the signal path, is crucial knowledge for any musician, recording engineer, and producer using Pro Tools. That knowledge will help you use your studio gear the way it was intended to work, enabling you to achieve optimal recording levels and help you avoid clipping or unwanted distortion. You'll also be able to troubleshoot just about anything in your Pro Tools studio signal flow. Let's follow the signal path from a vocalist to a set of monitors, that is the entire input to output signal path.
As the vocalist sings into the mic, the mic picks up that energy and converts the acoustic energy into an electrical current. The signal then travels to the microphone preamplifier in your audio interface where the signal is boosted in level. Next the signal is converted from analog to digital from electrical current into 0s and 1s. It goes into Pro Tools and is routed to your hard drive where it's recorded. Pro Tools then routes the signal back out to a digital to analog converter in your interface, where it's amplified and sent out to the monitors or headphones.
Let's take a minute to discuss gain stages. A gain stage is any device along the signal path that either boosts or attenuates the level of a signal. Here are the potential gain stages involved in recording an instrument or a voice with a microphone into Pro Tools, both on the input and output sides of the signal flow. First, we have the dynamics of the performance, how loudly the singer sings or the player plays his instrument. Then we have the instrument volume level and amp volume. If there are any effects in the signal path those also have gain stages too, then we have the mic preamp level or the line/instrument input level.
Finally, if you have a compressor in the signal path or any other post mic preamp affects, those will affect the input level. Once the track has been recorded into Pro Tools there are number of gain stages on the output signal path. Any plug-ins or inserts that you have on a track have their own gain stages, and if you've setup any effects loops you may have send levels or auxiliary track levels that also affect the output levels. Each track has an individual volume fader that will obviously affect the output volume.
The master fader track level determines the final output level of the mix, and then finally, you have the headphone or monitor levels that determine how loud you actually hear the output from Pro Tools. Now let's switch gears and talk about the MIDI signal path. MIDI performance data is played on a MIDI controller. The data goes into the MIDI interface, which may or may not be built into the controller itself, where it is converted into binary for Pro Tools to recognize and record. At this point the MIDI performance data still has no sound, then that data is routed to a sound source.
It could be a virtual instrument inside the computer or an external sound module. If it's a virtual instrument, the MIDI performance data stays within the computer, where it is transformed into an audio signal. If using an external sound module, the MIDI performance data is routed out of Pro Tools, converted back into MIDI data, and then transformed into an audio signal. That audio signal must then be routed back into Pro Tools via an audio input. Once it's in Pro Tools you can monitor it and record it as an audio signal, and all this happens in a fraction of a second.
So for both audio and MIDI data, the signal flow is pretty complicated when you really look at it through all the components. Understanding the signal flow and the gain stages along the way can help you capture higher quality recordings, as well as troubleshoot almost any signal flow and gain staging problem during the recording and mixing process.
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