Virtual Pickups Part 5

Recap

Last week, I presented the 4th part of the Virtual Pickups series. The article continues the series with the introduction of the preprocessor and how it negates the actual pickup’s natural comb-filter effect, with a result that is exceptionally rich in harmonics —very much like an acoustic guitar, with a sufficiently flat frequency response curve all throughout the audio frequency range. 

Here are audio clips of the raw (“Direct” unprocessed) sound vs. preprocessed (“Preprocessed”) sound:

Resonant Filter

As mentioned in Part 3 of the series, the electrical characteristics of the traditional pickup imparts a resonant low-pass filter effect, with a 12db/octave slope in the 2kHz to 6kHz range. Here are graphs of some pickups, including the active EMG81 and EMG85, the stock Stratocaster pickup, and some DiMarzio single and double-width pickups, vis-à-vis the Nu Multi (in blue). Notice the typical hump at around 2kHz to 6kHz for the passive pickups. This is the effect of the filter’s resonance, and pretty much gives it a very noticeable character. After the peak, the response falls off fairly quickly. Traditional pickups are low-fi, and do not extend the full 20kHz audio range. The EMGs, are more “hi-fi” with frequencies that extend further upwards the audio range, but has this peculiar fat and wide hump centered somewhere in the 1Khz range (orange and light blue).

These frequency responses can easily be modeled using resonant low-pass filters (one per pickup). Additionally, a high-pass filter can model the low-end response, which has a mild roll off somewhere in the 60-100Hz range.

The anticipated Ascend VPU provides controls for these resonant low-pass and high-pass filters, in addition to the standard tone control that most guitars have, which is another low-pass filter, but with a milder 6db/octave slope.

Modeling the Stratocaster

Using the pickup-position comb filters and the resonant filters, it is possible to get something really close to the sound of actual pickups. If the modelling is done right, you can even get results indistinguishable from the real thing.

To get a good model of a guitar’s pickup using the Ascend VPU plugin, I prerecord short audio samples of the target guitar for each of its switch settings, all using the same riff (or chord), same picking position and intensity. In the case of the Strat, I prepared five audio clips for each of the five switch settings. I then prerecord the same riff (or chord), this time using the multichannel pickup. Just straight to the audio interface. No effects. No EQ. 

Note: The Strat I used for testing is equipped with Dimarzio Injector at the neck and bridge positions and Dimarzio Area ‘67 at the middle position. The pickups are positioned at 6.1″, 3.7″, and 1.56″ from the bridge.

The Ascend VPU plugin is inserted in each of the six multichannel pickup tracks. The virtual pickups are positioned using actual measurements as a guide. After positioning the virtual pickups, I then adjusted the resonant filter settings to match the actual Strat recordings. This required some close listening. For each switch position, I played the actual Strat and multichannel pickup recordings, one after the other in a loop, to get a good A/B comparison, while dialing in on the control settings.

The resonant filter settings I find that are as close as I can get to that of the Strat are:

Here are the A/B (split) testing results. Each sound clip is a two part mix.

1. The first part starting at 0:00 is the recording of the emulated pickup.
2. The second part starting at 0:03 is the recording of the actual Stratocaster guitar.

So there you go. Listen closely. Can you spot the difference between the actual and emulated versions in the recordings?

Next time, in the last installment of the Virtual Pickups series, we will model other pickups, plus some more additional tricks you can do with the Ascend VPU plugin.

Oh, and if you have a special guitar and/or pickups that you want to model, feel free to send over audio recordings, exactly like the samples above, for all switch positions. Try to pick the strings at about 6″ from the bridge (just above the neck pickup for Strat like guitars) with the same intensity as in the samples above. Send them over and I’ll see what I can do. You’ll also need to tell me the exact pickup positions too and whether they are single or double coils. I’d add them to the presets list, if the guitar and pickups are notable exemplars. I’d love to get samples of various guitars!

Further Reading

1. Virtual Pickups Part 1
2. Virtual Pickups Part2
3. Virtual Pickups Part 3
4. Virtual Pickups Part 4
5. Ascend VPU User’s Manual