Welcome back everyone to Round 2 of Mastering the Mastering Process! Last time we discussed what exactly mastering was and what was involved in the process. While last time we discussed track sequencing, restoration, compression, etc. this time we are going to take things even further down the pipeline.
Also available in this series:
- Mastering the Mastering Process Part 1: Overview
- Mastering the Mastering Process Part 2
This time around we are going to look at Limiting and the concept of loudness and getting the album ready for pressing. The second half of this tutorial will require either a Mastering DAW or some other software that will be able to save the right format for CD pressing and add the appropriate meta data to the CD; we will cover what some of those DAWs are.
What is Loud?
Can you tell me what loud is? Is it a particular volume, say 32 on your car stereo? Or perhaps loud is a cough in a quite library? Something can only be defined as loud when compared to something else; without some other noise or sound we have no context. It would be like looking a sphere in infinite space with nothing else around to give you a clue as to how big the sphere actually was; is the sphere the size of a gum ball or a planet? When we Master in todays world we unfortunately are the culprits who proliferate the Loudness War.
The Loudness War is a constant battle amongst producers and artists to become louder than their competitors. Why? Because it is generally believed that if your album is louder it will be perceived as better and at one point or another that was true. But in today's world everyone is loud. And if everyone is loud how can you stand out from the rest of crowd?
Truth is you can't get any louder with today's audio because we have a hard ceiling that we cannot go past; this ceiling is called 0 dB or full scale. The digital realm of ones and zeros has its limits and if we pass this 0 dB mark we will hear horrid digital distortion. To keep pushing the limits however we are forced to induce limiting on our tracks which is essentially just extreme compression.
However if your limit too hard you will begin to hear distortion again just like you went past full scale. In addition, the harder you compress the less soft sections you have. If there are no soft sections to compare against the loud our ears will not actually perceive it as loud. Instead it will just sound like the life was sucked right out the music.
The reason for this is because we humans hear loudness in terms of RMS. This RMS (root mean squared) for our purposes is simply the average volume of a sound source. Sure peaks can get louder than the RMS but this change in average volume is what tells us what is loud and soft. When you over limit you are creating a sound that only has a high RMS and our ears adjust and get used to it. With no soft sections and peaks popping out of the RMS we simply are left with a bland constant volume.
I cannot stress enough how much it is your job to educate the client on why extreme compression and limiting is bad. Many producers and artists do not understand what effect it will have on their music. Another thing to keep in mind is that if they plan on having their music played on the radio there will be even more compression added after the fact by the radio stations.
Despite all of this, you also need to adhere to the client's wishes; if they are paying and want it compressed to hell and back then so be it. In this next section we will cover how exactly to go about limiting and compressing the entire album.
When contending with Limiting and making tracks louder there are a few things to keep in mind. You need too...
- Decide what limiter you will use.
- Decide whether you will use 'brick-wall' Limiting or 'soft' limiting.
- Decide if you will limit the tracks separately or on the master channel.
The choices you make here can have an noticeable impact on the outcome of the album. Deciding what limiter to use can be tricky or extremely simple. If you are looking to color the sound then I would recommend playing with different compressors and limiters and see which one gives you the sound you desire. However, if you are going for a clear mainstream sound then your options get extremely small; the L Series from Waves.
To say that these limiters are prevalent in audio is an understatement. For better or for worse they are the industry standard for limiting. The important part however for picking a limiter is whether you like the sound or not! If you are unsure about which to pick then go for the limiter that leaves the sound uncolored, as it will be the safest bet.
Let me make one thing clear when it comes to brick-wall vs soft limiting. You will always have a brick-wall limiter as the processor in your signal chain. You cannot afford to go over 0 dB and have that digital distortion. However that doesn't mean you can't use another limiter or type of limiting earlier on in the signal chain. This final brick-wall limiter will act like a safety net in case any peaks squeak on by. If you really want to make sure that you will be safe from digital overs then set the threshold to -0.1 or -0.2 to make sure it catches those peaks.
When using a limiter you will induce distortion. There is no way around that fact. However, brick-wall and soft limiting are going to have different kinds of distortion based on how they work. A hard limiter is going to give you the most volume but potentially the most distortion since it literally clips the signal into a square wave shape the longer it is above the threshold. A soft limiter will still distort the waveform but not induce such harsh clipping but the drawback is you may not get as much volume as you wanted.
When you actually begin to limit the material you should let the material decide whether you should limit the whole album from the master channel or do most of the limiting on each track before the master limiter. If all the material sounds a lot alike then you can most likely get away with only using a master limiter. However if you say working a compilation album of Top 20 hits then you may need to limit them individually first depending on how well you balanced them out beforehand. The important thing to take away is not to overdo it if at all possible. If something needs to be louder then ideally people would just turn the dial up. But alas the clients wishes will always rule out.
For examples sake I have included some examples of limiting on the tracks we used from last time. For all of these examples we will be using peak limiting as opposed to RMS. I will first start with some examples of hard limiting...
- First here is our example at full scale but not pushed past the limiter for reference.
- Now we will push the gain 2 dB past the limiter. Notice the slight distortion that creeps in every now and again.
- Next we will push the gain 4 dB past the limiter. Now the distortion is becoming much more prevalent.
- Finally we will push the gain 6 dB past the limiter. If you can't hear the distortion by now then you need get your ears checked!
So aside from the distortion, did we get any benefit from the limiting? Well if louder was your goal then yes. Our original RMS was roughly -15 dB, 2 dB past the limiter we moved to -12 dB, 4 dB past gave us -10 dB or so, and the 6 dB past left us at -8 dB. So yes things do indeed get louder but at the cost of some extreme distortion.
Next we will use the sample examples but using very generic soft limiting instead. After the soft limiter is still a hard limiter at -0.1 to prevent any digital peaks. Take a listen and tell me if you here the difference...
- 2 dB past
- 4 dB past
- 6 dB past
This time around our original RMS was roughly -15 dB, 2 dB past the limiter we moved to -13 dB, 4 dB past gave us -11 dB or so, and the 6 dB past left us at -9 dB. Obviously we still induced unacceptable distortion but not quite as much as with the brick-wall limiting. However we did not quite get as much RMS as before.
You do have other options for limiting such using the RMS level to indicate when to start limiting, using multiband limiters, etc. The choice is really up to you on how you wish to approach the limiting as different audio material will require different types of limiting. Just remember not to overdo it!
Meta Data and Shipping
Finally we arrive at the mythical meta data aspect of mastering. This is a process that most musicians don't even know about but none the less is still very important.
When printing an audio CD we have audio data, error correction, and meta data known as subcodes. These subcodes provide all manner of other features and functionality to the disc that the audio obviously cannot provide. These subcodes are organized into channels P, Q, R, S, T, U, V, and W and traditionally refer to this information as PQ information for short. Each of these channels will carry different pieces of meta data that will be read by the computer, CD player, etc. Traditionally with a audio CD you will only use the first two channels P and Q. Let's look at what these two different channels do...
- P - This channel contains any pause markers you may have placed in your sequence if your DAW allows it.
- Q - The Q channel will tell you what position you are in within a track or the album as well as the ISRC code information.
The ISRC stands for International Standard Recording Code and is a way to indentify recordings. Every published recording must have a ISRC code and even if the recording is used in another album, it will still have the same ISRC. In addition, different recordings of the same song will also have different ISRC codes; it is strictly for identifying the recording. These ISRC codes contain information such as who the track is registered to, country of origin, year, and a designation code. It is this ISRC information that will allow the tracking of sales of individual tracks, if they were played on a digital radio station, etc. so that the artists can get paid accordingly. If however you need to track the album as a whole you will then need a UPC code (barcode).
Your job as a mastering engineer is to put all of this information together so when the CDs are pressed they will have all the appropriate information. Only Mastering DAWs or other dedicated software can perform this park of Mastering Process (sorry no Pro Tools or Logic). Some of these programs are Samplitude, Sequoia, WaveBurner (comes with Logic), CD Architect, Pyramix, SADiE, and BIAS Peak just to name a few. Here is a good order of operations to go about when inserting all the necessary information...
- First insert all of the track markers (and pause markers if you are using them).
- Next add the appropriate information for each track marker such as ISRC, track name, composer, artist, etc. Also be sure to check copy protection and pre-emphasis if you intend to use them.
- After all of that add the UPC information to the disk as well as naming the CD.
Now would be a good time to burn yourself a copy and make sure everything works as expected. Keep in mind not every CD player can read the CD text information you entered, but never the less it is a good idea to include it anyways.
Finally we have reached the end of the line for the Mastering Process; getting the CD to the plant. Every CD plant has different protocols and formats that they will accept so always be sure to triple check that everything is in line and acceptable by their standards. However most plants will accept what is called a DDP tape or DDP file which is usually the safest way to get the information and audio to the pressing plant. Not all DAWs can export to DDP however so do be careful. Essentially the DDP file is a digital form of the CD that can be used as the Master for the CD plant to print all other CDs from. Most plants will allow you to electronically send this file to them via FTP but again check with them ahead of time.
Phew! A lot goes into Mastering as you can see. Some of it can very technical while other aspects can be very creative. Like everything else in our field, experience and practice will always render a better product in the end so keep at it!
Always make sure to keep your clients involved and to make sure everything is ready for pressing. Now that you know how to Master the Mastering Process, go master it! Thanks for reading!