While acoustic guitarists may love the tone of their favorite guitars, most are far less enthusiastic about how they sound when plugged in. Even the best pickups often fail to do justice to acoustic tone. That has been changing, however, due to a digital signal processing technique based on impulse response (IR), which makes it possible to capture the sonic signature of one sound and apply it to another. Using IR technology, it is possible to capture the natural acoustic sound of a guitar and then process the pickup to make it sound more like the instrument’s unamplified sound.
IR-based systems have been around for some time, but best results are usually achieved by capturing the IR of your specific guitar. Products that make the IR creation process accessible to guitarists have only begun to appear over the past few years. L.R. Baggs has recently thrown its hat into the ring with an impressive debut, the Voiceprint DI, a $399 preamp/DI that lets guitarists create and use their own IRs. The company is taking a bold approach with its first app-controlled product by leveraging mobile phones for creating the IR—known as a voiceprint—as well as for accessing advanced features of the hardware.
Impulse response features aside, the Voiceprint DI functions as a simple preamp/DI with 1/4-inch input and output jacks, XLR output, volume, effects insert, mute switch, and ground lift. The remaining controls affect the voiceprint: a knob as well as a footswitch for selecting among 99 possible presets, a knob that controls the blend between the direct guitar sound and voiceprint, and an anti-feedback control. Offering 24-bit, 96Khz A/D conversion and 32-bit internal processing, the 4.75 x 5 x 2.5-inch device has an input impedance of 2.2 megaohms.
Creating Your Own Voiceprint
The Voiceprint DI can operate without the phone, but first you need to create one or more voiceprints and load them into the pedal. Creating a voiceprint requires the free AcousticLive app and a Bluetooth-connected iPhone 6 or later. An Android version is expected in the future. The process is simple: Place your phone in front of the guitar, plug your guitar into the Voiceprint DI, and select Create Voiceprint in the app. The app prompts you to tap on the body of the guitar, play a few chords, individual notes, and scales, and finally, audition the result before saving it as a preset. If necessary, you can reposition the phone and try again—as with recording, different mic placements may produce slightly different sounds. The training process is fast and easy and requires no special gear other than the phone.
Advanced Sound Tweaking
While the above process performs the magic of transforming your pickup to closely match the acoustic sound of your guitar, the unit’s ability to shape and refine that sound goes further. The AcousticLive app allows you to adjust the volume of the processed guitar, control the blend between the voiceprint and raw pickup, adjust an anti-feedback control and a five-band fully parametric graphical EQ, and store everything as part of a preset. Amazingly, you can also access the Voiceprint DI through an Apple Watch, changing presets, muting or bypassing the pedal, and tweaking all the parameters of a preset, including the parametric EQ.
Rather than providing a standard notch filter, the AcousticLive app analyzes your guitar during training to identify resonant frequencies most likely to cause feedback. Turning up the anti-feedback control progressively cuts those potentially problematic frequencies. I found this control effective as a way to tighten up the sound even when not trying to control feedback.
The EQ (plus variable-frequency high and low-pass filters) is an incredibly powerful feature in its own right. The AcousticLive app provides a number of handy preset EQ curves that may be useful starting points, but you can also take total control to make significant changes to your tone by up to +/-15dB at each frequency. The voiceprint and EQ complement each other well. The voiceprint transforms the pickup in a way that would be impossible with EQ alone, eliminating quack and other unnatural characteristics we associate with pickups, while the EQ lets you refine the result, adjusting for personal taste.
Because both the Voiceprint DI’s firmware and the AcousticLive app can be updated, it is likely that we’ll see continuing improvements and features, and perhaps even new directions based on the device’s digital signal processing capabilities. lrbaggs.com
This article originally appeared in the July/August 2021 issue of Acoustic Guitar magazine.