Craft a vintage bass guitar sound using Logic Pro X’s built-in amp modelling plug-ins.
Mixing, recording and processing a bass guitar can be a real challenge. In this month’s Logic column we’ll look at how to achieve a bass sound that recalls the legendary 1969 Ampeg SVT amp and cabinet combination.
First of all let’s start with a quick check of the bass guitar itself. It’s vital that a bass guitar is well set up before recording begins to avoid wasting hours in post-production trying to correct problems. On a new audio track check the intonation of your bass guitar using Logic’s Tuner insert plug-in. One of the easiest ways to achieve this is to tune each open string and then to play the 12th fret (an octave above). If your bass intonation is correct, then both notes should be perfectly in tune. If this is not the case then you should adjust the setup or take it to a bass guitar expert to set it up for you.
One of the other things that examining the pitch with a tuner will reveal is the amount of pitch fluctuation from when you first pluck a note through to the end of the note decay period. Typically, thinner gauge strings — though easier to play — are more prone to pitch fluctuation. This results in a ‘boi-oing’ sound and a corresponding pitch swing when each note is plucked, since the pitch will always take a moment to settle down. If you notice the pitch drifting a lot then there are two ways to reduce this. One is to simply put thicker strings on the bass. The other is to play more gently or use a thinner pick. It’s worth being aware of these pitch fluctuations as they can create problems when trying to integrate the bass part into the track.
Now that you’ve got your bass guitar correctly set up, the next stage is getting a great bass amp tone. One of the most revered bass amplifiers of all time is the Ampeg SVT (Super Valve Technology), and there’s a good reason most big studios have one ready to wheel out. The 1969 SVT and matching 8 x 10 cabinet has a characteristically solid bottom end along with natural sounding compression, warm gritty drive and a presence boost that helps bass sounds cut through a mix. Let’s look at using Logic’s stock plug-ins to emulate the sound of a classic SVT stack.
Record a simple bass line or call up a track where you have a DI’d bass recording (see Audio Example 1 and 2 for a direct recording of a simple bass line played on a Jazz Bass using neck and bridge pickups). In the first insert slot add an instance of Logic’s Bass Amp Designer plug-in. Begin by loading the ‘Amp Egg’ preset. To enable us to focus purely on the amp sound go to the slider next to the Amp button and move it all the way to the left. Given that we are aiming for a classic SVT type of sound set the Amp drop-down to Classic Amp and the Cabinet to Classic 8 x 10. The Amp Designer plug-in GUI and control layout now mimics that Classic Amp setup.
The next thing to adjust is the microphone type and its position in front of the cabinet. Experiment with the different microphone types via the Mic drop-down menu at the bottom of the plug-in GUI (I settled on the Dynamic 421 microphone). Next, hover your mouse over the bottom third of the cabinet until an overlay with a picture of a speaker appears; the circle is the microphone position, dragging this to the right will take the microphone off axis and will result in a drop in the amount of high end, which can be really useful if you need to decrease the severity of the string attack. Adjust the position to taste.
Let’s now look at the amp controls in detail. To the left of the amplifier you will see the Channel (with options I and II) and Bright switches. These controls vary the timbre of the bass. For example, channel two has less bottom end than channel one, while the Bright switch increases the amount of top end quite dramatically. If you are new to the world of bass guitar I would suggest beginning with channel one and keeping the Bright switch off, unless your bass guitar recording is noticeably too dull.
Next, let’s tweak the EQ. The main controls are the Bass, Mid and Treble knobs. However, to get a wider variety of results each band can be switched to a different frequency range using the switches above. Bass Amp Designer has an additional EQ section that can be revealed with a button above the Master volume knob. This can also be switched between graphic and parametric modes. This section is good for a little final tweaking of your bass sound by applying frequency cuts or boost which weren’t possible with the Bass, Mid or Treble controls (see Screen 1 above and Audio Examples 3 and 4).
Now, let’s look at how to create a more aggressive variation of the same type of bass sound. We’ll achieve this by using the Bass Amp Designer to add a lot of distortion, then apply heavy filtering in a separate EQ plug-in to remove all of the excess top end. This yields higher distortion while avoiding harshness. Ultimately, the advantage of this technique is that it adds harmonic content in the mid-range that will help the bass guitar cut through a busy mix.
Return to the Bass Amp Designer plug-in and this time set up a much more distorted and aggressive sound. Next, add an instance of Logic’s Channel EQ plug-in. Open the Channel EQ plug-in’s editing GUI, turn on the low-pass filter and set the slope to 18dB per octave. Adjust the cutoff frequency of the filter to remove most of the harshness from the top end — I’ve set mine to 1780Hz. Also try using the channel EQ plug-in to emphasise the upper mid-range just before the filter kicks in. This is an old guitar EQ trick that works just as well on bass guitar (see Screen 2 and Audio Examples 5 and 6).
The next challenge is achieving a bass part that is consistently audible. Listen to your bass recording and identify where the levels of different notes vary without musical intent. We should adjust these notes so that they are more even in amplitude. If it’s only a few notes that require attention it is simplest to do this via region editing. Use the Marquee Tool to draw around any notes that are clearly too quiet and then click within that selection to create a new region. With the new region selected, go to the Region Gain parameter in the Inspector and increase the gain until the notes are correctly balanced. If your bass part has more general volume fluctuations and/or requires greater shaping of the decay characteristics of each note then it’s worth reaching for compression.
The compressor within the Bass Amp Designer itself really simple. Turn the Compressor section on then use the Comp knob to set the required amount of gain reduction. The LED to the right of the knob will light up to give you feedback when you are applying gain reduction. The button above the compressor switches the compressor between soft, gentle levelling or harder characteristics. Although this compressor is useful I generally prefer to carry out my compression duties in Logic’s dedicated Compressor plug-in.
The classic compressor to pair with a bass track is an 1176, partly because of its ability to apply vast amounts of gain reduction very quickly. On the next free insert slot add Logic’s Compressor plug-in and load the FET Bass preset. The Vintage FET model is a nod to the 1176. Tweak the Threshold control so that you are applying between 6 and 12 dB of compression (see Screen 3). You should notice an overall levelling of the bass part and an increase in the apparent sustain of each note. Increase the make-up gain until the bass part is at the same level as when the compressor is bypassed (Audio Examples 7 and 8). If you feel the compression imparts a useful volume lift but the end result is too drastic then go to the Compressor’s Mix parameter and use this to blend the original bass back in with the compressed sound.
That’s the basics of getting a good bass amp tone with a consistent level, next month we look at more bass guitar processing techniques moving onto insert effects and layering techniques.