Creating great guitar sounds on GNU/Linux

By Arda EDEN (ardaeden@gmail.com)

INTRODUCTION

Some time ago, when it was with proprietary software, I really had great electric guitar sounds by using non free fx-amp modelling plugins. Since I'm not touching any proprieary software for a long time, I was in the search of replacements for those plugins on free operating systems. At the time that I was giving up, I met JACK, LADSPAs, Ardour and many others and I saw that it was possible. This is an article about how guitar players can have a great sound while keeping their freedom in their hands.

The Project

This project is made to show that, great works can be accomplished by using free software and low costing gear. Now take a listen to the track below which is played and improvised by me, before/while reading the article (no amps or hardware fx processors are used, all of the work is done with free software and LADSPA plugins):

GNUitar_improvise.ogg

Some tips and tricks about the gear used

Whatever software and plugins you use, the sound source plays the most important role in overall sound. In this situation our sound source is the guitar it self and the other stuff (cables, preamp etc.) just before the soundcard. They don't need to be too expensive. There are some solutions. Take a look:

The Guitar

I never had enough money to have an original Les Paul or a Strat guitar. So I always looked for low costing solutions. Nowadays I'm playing a cheap Yamaha PAC 120 SJ which I paid nearly 300$ for. It has nice fretboard so I decided to modify it by changing the pickups. For the neck I'm using a DiMarzio DP190 which is known to be a clean and transparent vintage pickup, and for the bridge, I coupled the DP190 with a Seymour Duncan SH4 JB which has a harsher sound in order to have a good balance in between. Those pickups both are vintage sounding and has low output. I like low output guitars because I feel that I have the control on it. With high output pickups even a little touch of pick makes a high sound which is hard to control in the terms of dynamics. So my guitar became a 500$ guitar. Humbucker pickups have two kinds of connections. When connected in series they give higher output but poor high-end (trebles), in parallel they have lower output but the high end is more articulated. I prefer the parallel connection and did so. Now it's not just like a Les Paul but relatively close to.

The Preamp

Most of the semi-professional PCI sound cards have a line level (0 dB) input, but the guitar outputs are too low to match with, even if they are active. So you need a preamp to shift the output to line level. I advice using a tube preamp with digital outputs, so you can connect it to the sound card's digital input (if it has) to have a cleaner sound with minimum loss. I do not have one of those so I'm using my cheap Behringer 1622fx mixer as a guitar preamp. I jack my guitar to one channel, set the fader to unity gain (0 dB) and turn the gain (trim) to a nominal level just before clipping.

The Cables

The cables are more honored in the breach but they have an important role in the terms of noise. Use well screened and well soldered cables. Keep the audio cables away from the high-voltage power cords to prevent 50 - 60 Hz noise interference. Any intruded noise will always be with you. That's all I can say about the cabling.

The Soundcard

A high SNR (signal to noise ratio) card should be preferred. I'm using an M-Audio 24/96 for a long time and it's enough to me for now. Some external cards have their own instrument preamps on them, but it's adviced to be carefull about the ALSA (sound server for GNU/Linux) support. See http://www.alsa-project.org/main/index.php/Matrix:Main for supported harware.

The Software used

I'm an Ubuntu 8.04 user for a while. It's kernel has realtime support and works really fast. In this project I used Hydrogen for drums and Hexter for the bass. I played the strings track using my old Roland JV80 synth, realtime. Hexter is controlled by Rosegarden. Both Hydrogen and Rosegarden are syncronized with Jack transport so I could bounce them to Ardour, which is also syncronized with Jack. I focused on the guitars and did not pay too much attention to other tracks. I just used them as they are. Maybe just a little compression on bass to control it's dynamics.

The guitar FX BUS (most important part)

As I mentioned before this project is made by only using free software. So the LADSPA's play an important role here. There are too many LADSPA plugins written by saints (for me they really are), but CAPS Plugins are especially great with their vintage sounding guitar gear simulations.

There are multiple ways to create a guitar fx rack on GNU/Linux. Jackrack seems to be one of the solutions for this purpose. You can setup different plugins in multiple ways following the signal flow, store them and make various types of connections to other applications by using Jack's connection window. In this way you're able to lighten the load over DAW software you're working with, which is Ardour in this situation. But I didn't do that ! I setup my rack on a bus track in Ardour. Why ? Because, nowadays I'm having some problems with Jack Rack. Ubuntu 8.04 is new and all the problems are not solved yet. If I had used a stable release (7.10 was the last) of Ubuntu, I would prefer Jack Rack for this project.

I created a bus on Ardour ("Driven Guitar Bus" in this situation) and setup my guitar FX Rack on it. Why didn't I set it up directly on the track ? If I had to make multiple takes by using the same plugins, I would have to put them on every track I have. This would be a very processor consuming way. By setting up a bus, you can use it for every track just by simply routing properly.

This bus gets the signal directly from system capture device, which is a clean and flat guitar signal coming from the mixer and after processing it with the plugins, sends it to the related track we wish. But , Why did I choose those plugins ? and Why they are connected in that order ?

See below for details ....

The FX Bus Detailed

Our first plugin is C* Mono Compressor. This plugin is really great and acts like a little old fashioned which is suitable for starting to have a vintage sound. A compressor on the guitar, narrows the dynamic range and creates a steady and sustaining sound. The parameter values can change according to the guitar's response to player. With my cheap guitar this setting worked well. Notice the 12 dB gain here, this is also the first gain stage on the way to our driven guitar sound.

The attack and relase times are also important. A higher attack time will cause a late triggering and the compressor will respond slowly, the same is true for release time. It should be set properly so the compressor can stop working at the right time.

Your ear is your guide here. Just listen and set it up.

The low-end components of a signal occupies too much place and should be removed before any gain (distortion) stage. Otherwise, low-ends masks the upper harmonics and cause a muddy, colorless sound.

I did it from low-end to the high-end step by step in order to keep the balance. Very sharp EQ settings don't sound good.

The higher frequencies are boosted here to emphasize guitar's upper harmonics to produce a cleaner and brighter sound.

Those settings can also change dependently.

This plugin is actually our distortion pedal. The gain is increased 2.2 times. There will be a third amplifying stage after that, so the bass frequencies are cut a little bit more. The drive parameter also increases the distortion. This plugin simulates a tube type amplifier which emphasizes the second order harmonics and sounds thicker compared to it's solid-state counterpart.

The settings can vary according to how harsh the sound to be produced. I could not hear any difference when changing the temprature parameter so I just leaved it as it was.

This is the amplifier just before the speaker. The gain is increased by 1.5 times with a full drive and this plugin also simulates valve (tube) saturation. I set the tone parameter to 1 in order to keep the mid frequencies, and there's no change in lows here. Maybe just a little cut.

Watts parameter again did not make a significant change on overall sound and I left it as it was.

The gain and drive parameters can vary according to the desired amount of distortion.

Cabinet simulators are very important plugins because they give the signal it's final shape. CAPS Cabinet II offers many cabinet simulations but this time I preferred the Martial setting. It sounds a little bit Marshall to me :)

There's again a 5 dB of increase in gain to setup the final output level.

This plugin is here to compensate the low frequency loss in the previous stages. Lo gain parameter is set to 6 dB. Lo gain is an active low shelving filter and adds some low-end to the sound in a smooth way.

A little mid and hi gain is added just for final taste.

Discussion

What have we done till here ? and Why ?

To make great simulations, you have to think the real world. In this situation let's take a real studio and a recording engineer. The guitar is mostly recorded by microphoning the amplifier. That's where the acoustics join the subject. Inside the cables and amplifiers the signal does not contact with the acoustic surroundings, i.e. the recording studio. That's why I didn't use any time based FX processors on my bus. My bus, just simulates the electronic part of the signal's route, where begins on the guitar's pickups and ends at the cabinet speaker.

Creating the Depth

Let's now think about the microphone in front of the cabinet. Does it only pick up the vibrations of cabinet ? Absolutely NO. The sound radiating from the cabinet travels in the air, reflects from the walls or other surfaces - objects in the room and reaches the mic by mixing with the dry signal coming from the speaker. That's the magic which gives the sound it's taste. The reflected sound waves are a little bit delayed and when those delayed signals come together and mix with the undelayed dry signal, the phase differences between them causes a great colorfull effect in out ears and brain. This effect must be simulted with a short time, room type reverb. Don't use a long timed Hall, Plate or an Ambiance and a long delay directly on the dry sound. This is not natural. A short room reverb can be used either at the end of our Fx bus above, or in the first insert slot of the audio track. Short reverbs not greater than 200 ms, creates an acoustic surrounding around the dry signal. The reverb time varies depending on the size and the liveliness of the room. Don't forget to pass your reverb effect through a low pass filter. Don't forget that air absorbs the high frequencies. By simulating this effect, things can be more natural.

Room simulation diagram

Take a listen and compare the examples below:

without_room_simulation.ogg

with_room_simulation.ogg (TAP reverberator used on the master out with proper settings)

Turning back to my project

Just for the icing on the cake, I applied a little mixing to my guitar track. The 10 band EQ below is used just to compensate the low frequency loss on the FX bus and also necessary for sticking out the guitar in the mix.

10 Band Eq on mix

As it can be seen from the picture, the 125 Hz is boosted to make a thicker guitar sound and to create a nice sounding effect on sweep picking. 500 cycles is also boosted to emphasize low mids. At the high - end 4k and 8k frequencies are boosted to articulate the higher harmonics of the distorted guitar.

Below there's an amazing effect that I used to create more depth and interest. CAPS C* Scape really creates an interesting sound scape behind the guitar. It melts inside the mix and acts like a sequential analog synth playing in the background.

Click for audition of C* Scape:

c_scaped_guitar.ogg

Finally for the depth and interest a TAP reverbator just suits well.

TAP Reverberator

A nice high definition Hall algorithm, when combined with the C* Scape ..... there's nothing more to say. Listen the final shape :

final_guitar_sound.ogg

Below is my mixer screen (click to enlarge):

A few last words to say

One can say that better results can be taken by using any hardware processing. They're absolutely right. The purpose of this article is just to show that there are free replacements for the proprietary sound processing software, which can give the same, even better results when used properly.

I never believed the plugin manifacturers claiming that their software can simulate real analog devices perfectly. I know so many engineers that have worked both with the hardware and the software versions of some analog devices saying that, there's no similarity in between. I also agree with that. Today, free software is powerfull enough to satisfy musician's needs.

For any comments and questions please write to ardaeden@gmail.com