A/D and D/A Conversions

by on Aug.22, 2010, under Music

A point often overlooked by home recording engineers is that for every digital unit in an analog instrument chain an A/D and D/A conversion is being performed. Doing this once or twice with high quality converters is probably not very noticeable, but chaining several digital pedals together is probably not wise. Each pedal will do a full round of conversion and introduce their own ‘flavor’ of signal degradation.

Most home recorders are already converting twice by necessity, getting the sound in and out of the computer. Intuitively, it makes sense to leverage analog processing whenever they’re appropriate to avoid these additional conversions prior to the sound interface. The other option is to record dry and use digital processing ‘in the box’ as there are no additional conversions in this case. There are no shortage of high quality software DSPs.

Most folks, including myself, likely have more pressing problems to address in their home studio. However, A/D conversion is certainly a factor to consider before mindlessly stacking another gadget on the signal chain. Think about where in the chain the gadget is being placed. Could the number of conversions be reduced by rearranging the chain? Could this gadget be placed in a digital loop with the sound interface, thus avoiding another conversion entirely? Most modern rack-mount DSPs do indeed have this capability.

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Guitar Cabinet Simulation

by on Aug.18, 2010, under Music

The amount of ‘color’ imparted to a distorted guitar sound by the speaker cabinet is often understated. Guitar speakers are not high fidelity. Rather they’re designed to roll off high frequencies, typically those over 8khz or so, and usually have poor response to frequencies under 120hz. The high frequency attenuation is particularly important for high gain distorted styles. If absent, listeners will suffer fizz and sizzle.

However cabinets present problems. They’re expensive, heavy, and need to be driven loud to impart the impulse characteristics associated with modern metal and rock. This doesn’t gel with living in a 900 sqft house in a major metropolitan area. Many home recorders and musicians need an alternative.

One alternative is to simply record via the line out on a pre-amp…this sucks big time. You can compensate a bit with high and low cuts on an EQ but it will sound very thin and fizzy. Leaving the power amp in the chain and brining the signal back down to line level through a load box and speaker simulator is better. Many of these units feature adjustable high cut and voicing controls. Additionally, you retain the color of the power amp section. But the results are usually still disappointing. There’s something missing, speaker impulse response.

The sound heard on most rock and metal recordings of guitar is the result of miking a speaker cabinet. Without a cabinet in the chain, it’s virtually impossible to reproduce certain dynamics captured by the microphone. Enter speaker impulse samples. Thanks to Prof. Fourier, it is possible to tease apart the speaker impulse data for all possible tones given any guitar speaker. These impulse ‘deconvolutions’ may then be convolved with any digital audio track to replace the otherwise missing impulse dynamics. Several ‘convolution reverb’ plug-ins are available for the task.

With well captured data from a good cabinet and microphone, the results are amazing compared against the unprocessed track. Many free guitar speaker impulse deconvolutions can be found via Google. At least one free convolution engine exists for Linux platforms, jconv, and can be integrated with Ardour via the Jack protocol. I highly recommend anyone recording guitars direct-to-console check these tools out.

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Song Demo 1

by on Aug.09, 2010, under Music

Here’s a song created using the Ubuntu Studio tool chain discussed in previous posts. The drums are programmed using Hydrogen but the guitar and bass are real instruments. Both were recorded ‘direct to console’ with the bass going through a Sansamp NYC. The guitar chain is Engl 530 -> VHT 2/90/2 -> Palmer ADIG-LB (load box).


This was after spending about a month’s worth of solid weekends learning the tools and reading some advice from professional metal producers/engineers. In the field of sound engineering, I’m still very green.

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Gear Research Syndrome

by on Aug.01, 2010, under Music

I’ve been reading a series of informative and entertaining articles on home recording by Brandon Drury. The articles say less about what ‘to do’ and more about what ‘not to do’. This is not a criticism, rather it’s very appropriate for this craft. One particular pitfall illustrated, under which I’ve self diagnosed, is Gear Research Syndrome. Countless hours studying details of amplifier design, tube characteristics and other issues that have much less impact on an overall mix than many non-gear related issues.

Symptoms of the disorder include attention on manufacturing differences between Russian KT88 tubes and various knock-offs at opposed to important factors such as the instrument, skill, and the physical recording and monitoring environment.

Cognitive behavioral therapy is indicated in any instance of this disorder. The individual must be trained to recognize the excessive research behavior and reduce the amount of gear research. The additional attention redirected to more important issues will result in sound improvement and reinforce the behavioral change.

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Sweetening Metal Drum Tracks

by on Jul.19, 2010, under Music

Contemporary metal drum tracks sound pretty far from natural, they usually sound more like heavy grade pyrotechnics. When one first sits down to reproduce this sound it can be fairly daunting. Whether mic’ing a drum set or using software samples, raw drums are going to sound thin compared to what ends up on modern metal albums or in concert acts that mic the set and apply processing on a per channel basis. I’ve found a couple tricks that seem to work well for getting closer to the ‘over the top’ punch and smack adored by metal fans. My experimentation has all been performed on Hydrogen with LADSPA effects.

The Kick
Metal mixes will often synchronize the kick attack, a bass guitar attack, and a staccato attack on guitar simultaneously for a super non-syncopated punch effect. The kick is often on top of all this in the mix and that takes a ‘big’ kick that’s ‘perceived’ as ‘deep’. There are a couple do’s and don’ts here.

First, chorus works miracles on kicks. Apply it to the kick and only to the kick. Play with the settings until you achieve the desired size of balls. I’ve successfully used a multi-voice chorus LADSPA plugin to this end. The A-B difference is extreme. Mixing the chorused signal with the dry signal will help preserve the kick punch/attack. A 50/50 mix has worked well for me.

Next, I think it’s generally good to avoid reverb on a kick as it can kill the attack. I’ve heard it used effectively on older ’80s metal but it seems uncommon in modern metal, where the ‘fist in the face’ punch takes precedence. If it is used then the wet signal should be mixed with the dry as to preserve attack.

The snare seems much more variable, even amongst a sample of closely related metal bands. Tuning can vary quite a bit as can the level with respect to the overall mix. However, I’ve found that the careful application of plate reverb can effectively spice up a snare hit, specifically in sampled kits. I’ve used a LADSPA plate reverb that includes some filtering allowing for adjustment of sonic characteristics as well. A formerly ‘stock’ sounding snare blast now possesses an almost ‘gunshot’ like quality. And that’s what we metal folks like; the drums that sound like the 4th of July.

Cymbals and Hats
Thus far it’s my experience that cymbals sounds good relatively unprocessed. Some EQ may be in order depending on the situation, but I don’t see much point in toying with the natural resonance with reverb or anything else per say.

Toms are still a bit of a mystery to me. I’m not particularly happy with results I’ve achieved thus far. The toms seem to lack in pitch characteristics and sound ‘flat’. I’ve experimented with reverbs, which didn’t provide good results. Perhaps something to broaden the frequencies like pitch shifting would help. It’s also possible that I simply have poor tom samples. Anyone who would like to chime in is certainly welcome!

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The Ultimate ‘Free’ Music Home Studio

by on Jul.18, 2010, under Music

Certainly, there are many approaches to building a home studio depending on goals, stylistic constraints and monetary resources. My aim is to configure a digital tool chain capable of professional grade digital and analog source recording, whether I have the skill to produce a professional grade master is another matter entirely. This article shall focus on the tool chain, not the sound engineer’s skill. My personal music taste is ‘wall of sound’, classically infused, progressive metal. This style, and many others, requires a sophisticated chain allowing an arbitrary number of tracks from a variety of sources and the ability to manipulate tracks in a complex manner. This can all be accomplished at minimal cost using the tool chain outlined here.

I will take a ‘big-picture’ approach and outline how a number of different software applications are used together to achieve a sophisticated tool chain for recording music. I will not cover the operating details of each individual tool. However, I will reference external resources such as documentation and tutorials. Each individual tool has a learning curve of its own and will require time investment.

The Foundation
A personal computer running a Ubuntu Studio; a ‘mostly free’ distribution of the Linux OS geared toward multimedia production. It features a low-latency kernel that allows real-time monitoring while recording an analog source. Unless otherwise specified, it includes all the software discussed below. A reasonable quality sound interface is also required. Generally, a consumer grade sound card geared toward gaming is not appropriate. A sound interface designed for recording music with support for multiple balanced line inputs will save a tremendous amount of hassle and preserve fidelity. Many ‘pro’ and ‘prosumer’ grade interfaces use firewire to communicate with the PC. For a list of all supported firewire devices, click here. I personally use a Focusrite Saffire 4-in/10-out. Beware of Motu interfaces. They have a poor reputation with regards to supporting the Linux community.

The Plumbing
Browse the Ubuntu Studio menu and become familiar with it’s layout and contents. One of the items is ‘jackcontrol’ or ‘qjackcontrl’, a software version of a studio patch-bay. Consult the Jack Quick Start guide for an overview of basic functionality. Ensure that your sound interface inputs and outputs are visible from within jackcontrol before continuing. This application allows all other components of the studio to communicate with each other. It is the cables running from box to box in a physical studio.

The Kitchen
This is where it all happens. The Ardour application is a muti-track audio mixer/recorder with extensive track editing facilities. It communicates with your sound interface via Jack and can synchronize with all other sound applications, such as drum machines and sequencers, over the Jack protocol. Besides mouse and keyboard, Ardour can be controlled via external surfaces such as Mackie or Tascam mixing consoles. Enough information to get productive with Ardour is available through their online documentation.

Ardour supports LADSPA (Linux Audio Developer’s Plugin API) for effects processing modules. For most users, Steve Harris’s library will be more than enough to meet processing requirements. Effects can be added and removed from individual tracks via Ardour’s mixer console.

If you plan to record mostly ‘real’ audio sources, i.e. non-midi, then your sound interface + Ardour may be all you need. However, most folks don’t have a fully mic’ed drum set handy and many will want to emulate instruments they don’t actually play or own themselves. For these purposes, some additional software is required.

Instrument Sampler
Linuxsampler is capable of playing ‘.gig’ or ‘giga’ format instrument samples which was the format of some of the highest quality sample libraries. I say ‘was’ since Tascam discontinued in-house development of the format. However, development continues within the open source community. Regardless, giga samples are still widely revered in terms of quality today and many libraries remain available. Although the tool is free for non-commercial use, one generally must pay for the instrument libraries, which can run in the hundreds to thousands of dollars. However, a fantastic concert grand piano is available on the Linuxsampler site free of cost. Due to the software license, Linuxsampler is not included with Ubuntu Studio and must be downloaded from the Linuxsampler site.

The caveats aside, it’s the best sampler I’ve been able to find for the platform. Linuxsampler is a command line interface, so I recommend installing JSampler as well (also on the Linuxsampler site). This provides a graphical interface to the sampler engine. Consult the Jsampler documentation for installation and usage details.

Midi Sequencer/Tracker
Alright, we now have a nifty sampler that can be patched to Ardour either via the ‘mixer’ window or Jack directly, but there’s a catch. Ardour does not currently support midi-tracks. That is, the recording of midi data rather than the raw audio coming from the sampler. Capturing the midi data is ideal because Ardour can play back the track, using it as a midi source, into the sampler allowing different instrument setups to be substituted. If the audio is recorded then we’re stuck with that audio. Preserving the original midi-data provides extensive flexibility for re-mixing at a later time.

Enter the application Muse, a midi/audio sequencer. Rather than directly recording the audio output of the sampler with Ardour, we’ll patch the midi controller (i.e. a midi keyboard) to Muse, patch the output of the muse midi track to the sampler, and patch the sampler output to Ardour. Muse is responsible for capturing the midi-data while Ardour optionally records the audio simultaneously. If we’re unsatisfied with the instrument or sampler settings, the midi track can simply be played back in Muse with different sampler settings and re-recorded in Ardour. Muse also provides editing facilities for midi data.

The documentation for Muse is sparse. However, there are some decent tutorials to gain quick productivity. In particular, see Tutorial 2 that is relevant to patching Muse to an external sampler.

Drum Machine
Traditional hardware based drum machines are about as fun as drilling into concrete. To track a sophisticated song takes so long you just end up not doing it; the interfaces just stink. At least from my perspective, this all changed with Hydrogen. I don’t recall even needing documentation to begin using it, but a good manual is available on the site. A number of alternative drum kits are available, including a ‘death metal’ kit. Hydrogen will synchronize with Ardour over Jack. Mixing and panning of each individual drum piece can be performed through Hydrogen’s mixer. Like Ardour, Hydrogen also supports LADSPA plugins. When satisfied with the drum track and mix, just patch the output of Hydrogen to Ardour using jackcontrol and lay down the track.

Personally, I consider ‘mastering’ the art of ‘pulling the tracks together’ to sound like a cohesive performance rather than x-consecutive weekends in front of a computer. Many people would actually classify this as part of the mixing process. Either way, it can be accomplished by ‘mixing down’ tracks in Ardour, possibly with some EQ or reverb plugins.

The other side of mastering involves loudness control and saturation of the dynamic range; ‘filling the sound space’ to produce a sonic perception of ‘fullness’. The tool for this job is JAMin. It provides a suite of filters, limiters, EQs, analyzers and other processors. Tracks are routed from Ardour to JAMin and then back to Ardour. Tutorials are available on the site.

One part of the chain excluded from this discussion is tools to take the final master track from Ardour and publish it to one of many formats, mp3, CD, etc. This is because I’ve not yet reached this phase myself as of this writing. I’ll be sure to report my findings in a future update to this post.

The best of luck and satisfaction on your own musical endeavors!

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