A simple approach to mixing a rock song: Part 6 - Reverb

admin: First posted on 2007 07 13

Reverb? Sure, but how much and which one? Reverb is needed. Our biggest mistake when releasing our first album was leaving it semi- dry and boring. We should have added more reverb to our songs. First, our songs would have been livelier as that is what reverb does – it simulates the real life effects of a sound in a room, a club, or a concert hall. Second and equally important – most music that we listen to has reverb artificially added and so that is what our listeners are used to. Our songs sounded "unnatural" with little reverb.

The reverb is a very complex phenomenon. Sound bounces from walls, furniture and so on and comes back in many reflections, which may be indistinguishable from each other and which interact with each other. This is the simple explanation, but a reverb has many properties:

1. The total length of the reverb is defined by how long it takes for the reflections to stop. Reflections in larger rooms will take longer to bounce back. Reflections in rooms with very reflective surfaces will take longer to quiet down;
2. The attack time of the reverb is the time it takes to build full strength. The attack time is related to the total length as in natural reverbs short total length means short attack times and long total length means long attack times;
3. Smoothness or diffusion is described by the fact that some reverbs have fewer spaced out reflections that are easier to distinguish, whereas other reverbs have more reflections that create one smooth sound blob. This can happen as some rooms are empty while others contain a lot of objects and obstacles;
4. Irregularity happens because there is a difference between singing, for example, in the center of the room or singing next to one of the walls. The sound reflections in the first case may appear smoother, whereas being close to an obstacle in the second case may create pronounced reflections at specific times, creating a more irregular reverb;
5. The absorption of the reverb is defined by how much of the sound bounces back, i.e. by how loud the reverb is compared to the original sound. Certain walls will reflect sound better than others; and
6. A reverb has coloration as not all frequencies are reflected equally. You may, for example, get strong reflections of higher frequencies than of lower ones.

So different reverbs have different qualities. Since also some of the sound reflections that you will get will be reflections of reflections and not of the original sound, different portions of the same reverberated sound will also have different qualities. The tail end of the reverberated sound will sound differently than the beginning. Specifically, you will see in a lot of literature a software talking about the early reflections in the reverberated sound versus the late reverb.

At some point you will end up having to use an artificial reverb. The qualities of the artificial reverb console may be named differently, but some or all of them will be there. Rather than absorption you will see the wet / dry mix. Rather than coloration you will see equalization, or a high pass cutoff. Rather than attack time you may see room dimension. Rather than irregularity you may see left / right perception, and so on. One way or another, you will have to choose some settings that appeal to you, knowing what you know about what the controls mean. In our quest for a natural sounding reverb we did not always know what settings are natural. For example, we would not try to compute the total length of a reverb in a 10 ft by 10 ft room in which the singer is in the middle, the sound travels by 300 m/s, and the reflected sound carries 30% of the original sound amplitude when reflected by the wall. It is good to know, however, that if our reverb has distinguishable echoes which we do not like, we can increase diffusion. If the reverb is too much, we can decrease the wet mix. If the song is too loose, we can decrease the reverb length and attack time. If we want some end tail frills, we can change the reverb irregularity.

Now that we have talked enough about the qualities of the reverb, we have to find a good but cheap artificial reverb. A cheap one does not exist. Somewhat cheap options are plenty: 1) people swear by the reverbs produced by Lexicon; 2) some people like the reverbs in Native Instruments; 3) I actually like the reverb on my Line 6 POD; 4) similarly, I remember liking the Vox ToneLab reverbs; 5) any multi-track recording software will come with some reverbs – CakeWalk, CoolEdit Pro (i.e., Adobe Audition), Nuendo, ProTools LE, and so on; 6) some soundcards will come with reverb built in their control consoles; and 7) there are various VST or DirectX plug-ins.

My experience is limited mostly because, once I found something that worked and was easy to use, I gave up on anything else. We started with the DirectPro 24/96 built in reverb, but quickly found that we could not control much of its qualities. We then moved to the CoolEdit Pro reverb, where we did not have much luck funding a natural sounding reverb. The best reverb that we got out of CoolEdit Pro was using the Full Reverb at the Small Club pre-set but with smaller total reverb length (900-950 ms rather than 1250 ms); accordingly smaller attack time (around 55 ms); diffusion around 600 (in retrospect it should have probably stayed at 800); different mix (90% dry, 15-20% early reflections, and 25-35% wet); and different coloration (this reverb is equipped with a 3-band parametric equalizer in which we lifted the high band up, usually more than 5 dB. Incidentally we stopped using this reverb because we thought that its coloration introduced noticeable sibilance).

Nowadays we use the Line 6 PODxt and usually its Fender Deluxe Spring and King Spring reverbs. These reverbs seem to do the job for us. They do not have many controls. We cannot set, for example, the attack time independently of the total length. We cannot control the smoothness of the reverb. Even so, the reverbs seem to be designed well enough to sound natural.

Once we chose a reverb we had to figure out how to apply it. The reverb should probably come in after everything else, especially compression (even though on one weird slow song we had a good mix with a soft-knee compression after a good size reverb). With this in mind long time ago we started by simply applying reverb on the overall mix. Interestingly enough the reverb that we used always removed our panning, so we had to apply it separately to the left and right channels, which always made it sound different. There is nothing wrong with applying reverb to the overall mix, but we decided that the better thing to do is to apply the reverb separately to each track that needs it. There are two reasons to do that: First, there are some instruments that do not need a reverb, such as the bass. If you apply reverb on the overall song, you can still leave the bass out of the reverb with proper equalization (i.e., with a high pass filter), and you will only reverberate bass overtones. This may or may not be a good idea. It is probably the natural thing to do, although it may clutter your mix. Second, if you treat each track separately, you can apply different reverb to different instruments. You can, for example, give more to the solos, less to the riffs, and even less to the drums.

On one recent rhythmic loose song we ended up with the POD Fender Deluxe Spring reverb at its original settings and at the following "effect" knob settings: solo guitars at 4 1/4, rhythm guitars at 4, vocals at 2 ¼, dry snares, hihats, cymbals, and toms at 3 ½. On a slower song we used: solos at 7, riffs between 4 and 6, vocals at 2 ¼, hihats and crashes at 3 ½, snares at 2 ½. We did not choose these numbers randomly, but rather listened to each individual track to see how it sounded reverberated and chose the proper reverb for each (we were basically putting as much reverb as we could without having it sounding annoying). Choosing just how much reverb you want is a matter of taste and tastes are changing. If you listen to music from the 60s and 70s, you will notice a lot of reverb. In the 90s engineers chose less, sometimes to the point where the song mix sounds different, but the reverb itself is hard to distinguish. As usual, it is a good idea to listen to the mix of a professionally recorded song that you like. Last time I mixed a slow bluesy song, for example, I started by listening to the "The Thrill Is Gone" by B. B. King.

The reverb is complex and often used effect. So there is a lot more to be said about reverb. Here are some interesting questions: If we apply different reverb to different tracks, shouldn’t those reverb lengths be related somehow? Is it good to relate the reverb length and attack to the song tempo? What types of reverbs are out there? All this will be left for some other post.

authors: mic