Using Impulse Response Technology to Recreate the Sonic Characteristics of Analog Microphone Preamps and Acoustic Spaces

The study of impulse response technology allows audio engineers to attempt to recreate the tonal characteristics of a certain device. The purpose of this project was to recreate a sonic representation of analog microphone pre amplifiers and acoustic spaces through the use of impulse response technology. By creating these impulses, the student will attain the sonic characteristics of professional grade audio devices with impulse files, be able to enhance his recording and mixing capabilities, and create new and innovative sounds using these audio files. Introduction: An impulse response refers to the reaction of any dynamic system in response to some kind of input. Study of impulse response technology has been prevalent within the audio world for the last decade. Impulse response technology has been used for several different purposes. It has been discovered that with this technology one can essentially recreate an acoustic space, or device using certain techniques. By sending amplitude of signal through a certain device you can record its time and tonal based characteristics, therefore giving you a representation of the signal through an impulse response. This impulse response can then be added on to any audio track within a digital audio workstation by the use of an audio plug-in (Figure 3). The study of impulse response technology has benefited audio engineers and students everywhere. Students now have the capability of capturing any acoustic environment and digital reverb device they want. Studies correlating impulse response technology and analog microphone preamplifiers are extremely limited. Certain techniques allow you to recreate the sonic characteristics of digital reverb devices and the same techniques can be used on analog microphone preamplifiers. Two techniques that allow you to accomplish this are the Time-Pulse Technique and the Frequency Sine Sweep Technique. The Frequency Sine Sweep Technique is a generated time based sine sweep of the human aural spectrum (20Hz-20kHz), which documents a representation of the device via impulse response. The Time-Pulse Technique is a short waveform spike, lasting a few milliseconds, that is played through the specific piece of outboard gear documenting a representation of this specific device via impulse response. These two techniques allow for two different styles of documentation and representation to provide a comparison for the best results possible. Technique/Listening: Frequency Sine Sweep Technique: Generating a time based sine sweep allowed for the documentation of the signal to noise ratio over a selected length of time, ten seconds. Patching the audio output into the input of the preamp supplied the preamp with enough signal to properly document the preamp signal. Taking the output of the preamp and patching it back into the input of the audio interface connected to your computer resulted in the recording of the preamp signal. Fuzz Measure Pro is an audio program that allows you to take a frequency specific sine sweep (20Hz to 20kHz), send it through a device, and deconvolve the returning signal from the preamp into an approximated impulse response of the analog preamp. Time-Pulse Technique: Creating a pulse of amplitude with a length of milliseconds allowed for a suitable signal to noise ratio, which can capture the transients over time of each preamp. Sending this pulse of amplitude, through a Digital Audio Workstation (DAW), into the input of the preamp resulted in the impulse response of that preamp. Taking the output of the preamp and patching it into the input of the Digital Audio Workstation resulted in the recording and documentation of signal and harmonic distortion through the preamp. This process allowed for accurate analysis of the sonic qualities of the