Sound System picture courtesy of Yaniq Walford (Creative Commons)
Bass mastering is something that is discussed online from time to time and provokes a lot of interest, this is highly likely because getting the bass frequencies to sit right in your music can be a challenge for many engineers, musicians and producers across the globe. I am going to assume you work with a music style which has a natural tendency towards heavy bass, great… this is going to be for you.
As such you do not ‘master bass’ but work with in context of an overall musical balance. From the outset when it comes to bass mastering I will be extremely clear. There are 2 technical aspects that you must ensure you have under your control in order to ensure the bass levels and balance are perfect in your music tracks.
The phrase bass mastering means different things to different people and the 2 most common concerns are mastering bass in a music track, in terms of mix balance and also in terms of the final audio mastering process before music is released. Whether your concern be in your music mix down or in relation to professional audio mastering, good low frequency decisions require 2 important considerations :
1) Accurate loudspeakers
2) Significant bass trapping within the room
I cannot stress enough that the above aspects 1 and 2 are extremely important when judging bass levels. What you hear and any remedial processing actions will rely on the accuracy of what you hear. Without accuracy it is easy to compound issues in the low end response of a piece of music. With accuracy of room and monitors much more effective decisions can be made. The types of audio processing associated with a full, yet clearly defined low end response will all be easier to manage with accuracy of monitoring. Without it there will be continual wondering as to why your low end does not quite cut it. Low frequency processing such as side chaining your bass line with your kick drum, discrete equalization techniques, compression and harmonic synthesis will be easier to apply at mix time with linear low frequency monitoring.
Accuracy of loudspeakers or studio monitors
A small set of near field monitors typically have a response down to approximately 50Hz. Below this frequency the energy that is reproduced by loudspeakers is often diminished significantly (especially with certain loud speaker designs). This is in part down to the size and efficiency of the low frequency driver and cabinet combination. Near fields, being relatively small will often not have sufficient output to be able to allow effective judgements on mastering bass.
One way to increase output is to design a loudspeaker which has a reflex loaded port. These are usually a plastic cylinder which goes into the speaker cabinet. This creates a resonant filter type arrangement around a tuned frequency. This produces additional low frequency output. However only the best bass reflex designs (using costly R&D) avoid some compromises which apply to this type of speaker. Bass reflex ports tend to produce a resonant peak around the tuned frequency which can produce unwanted misrepresentation of the low frequencies present in the signal. The port whilst presenting enhanced bass output skews the response from being as accurate as a sealed enclose design. This must be considered when using a reflex loaded speaker. At Safe&Sound I use PMC IB1S transmission line speakers which have useful output in room at 25Hz and do not suffer from bass reflex port issues.
Acoustic treatment for the low frequencies
Untreated rooms have what is known as ‘room modes’ this is a natural but inaccurate response of any given room created by the reflection of low frequency signals from room boundaries. In a typical bass line and heavy kick drum the varying notes and sub energy will trigger a node related to the rooms dimensions vs the wavelength of the note.
All frequencies have a wavelength, those most troublesome have a wavelength of one of the room dimensions (or multiples of it) be it depth, height, length or diagonal paths (diagonal paths known as tangential modes). Such modes can be significantly reduced by installing bass traps. There can be very complex phase interaction between direct (from the speaker) and reflected waves producing a recipe for an unpleasant and inaccurate acoustic ‘soup’.
There are numerous designs some of which are quite complex. The simplest type of bass trap for studios are known as broad band traps. These are used in order to absorb some of the low frequencies and stop them from reflecting from boundaries back into an area where music is being monitored. This has the effect of making the low frequency response at the monitoring position more linear.
Subsequently it means remedial approaches such as equalization are possible with confidence. I have meticulously treated the studio here with very large amounts of broad band bass trapping. For some this is practically difficult to achieve but I knew it was an extremely important aspect of ensuring the accuracy of the low frequencies when bass mastering in context of a mix. You can see just one of the 7 large upright bass traps in the following YouTube video.
These are full corner infills from floor to ceiling and really trap significant energy and stop a lot of it being re-released into the room.
The above fundamental technical considerations will eliminate many issues people have with their kick drum and bass line / sub bass line. Practically an ideal monitoring situation is not always possible, so mix appraisal advice from a mastering engineer can be invaluable. In some situations stem mastering can also be an option as well (see the link below). There is always a way to get the results you require.
Clarification of the term ‘bass mastering’
Bass mastering is somewhat of a misnomer as you tend not to master bass, you work with it in context of a tracks mix down. During audio mastering with a stereo mix file a mastering engineer will spend ample time addressing any troublesome bass problems. In some instances a mix tweak can be requested to remedy stubborn issues (at Safe&Sound Mastering free mix advice is offered) Sometimes a little targeted equalization can work wonders and a few other more complex dynamic processes can sometimes be used in conjunction with low end equalization.
In these days of modern music production we have numerous bass music forms. To name a few the Grand Daddy of bass music, reggae, which would originally have had heavy bass guitar then we have newer styles such as drum and bass and dubstep, both heavily influenced by reggae music. Newer forms of music will have electronic influence and so in many instances you will have synthesized or sampled bass lines. Some tracks may be produced with a bass channel and a sub bass channel for those extra deep B-Line lows. Most dance music forms have a tendency for a well rounded and slightly heavier low end than a pop song for example. So with these bass music forms it is very important that the low end of a track translates well across the sound reproduction systems it will meet.
When mastering for music forms with a propensity to a full bass weight the mastering engineer will still have to consider where the tracks will be played. Too much bass and you restrict perceived volume goals, cause club limiters to trigger and may adversely affect FM broadcast processing. Too little bass and your track will sound thin and lacking in power. Getting the right balance is a combination of a good mix down, targeted tweaks, skill, correct deployment of tools and accuracy of monitoring in mastering. At Safe&Sound mastering we take a pro-active approach to assisting clientele and hope to help getting a perfect low end response for your music tracks and their respective genre.
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By Barry Gardner