Most vocals need to be compressed, but the amount used will be dependent on the style of singing and the singer .
Compression and equalization, which are two separate processes, are necessary on most music while working on it in a recording studio. While rap vocals are often staccato and compressed by nature, they are competing with very bass-heavy beats and need to stand out on the track itself. Accentuating the higher frequencies can make the vocals sound clearer, while compressing them heavily can help them stand out and be heard over the music, which is often secondary to what is being said in this poetic form of musical expression.
Instructions
1. Listen to the vocal track soloed first to get a gauge of what equalization and compression will be needed. Most rap is rather punchy in delivery and will need to be assessed by itself as well as with the music. Un-solo the vocal track and listen to it with the rest of the music. You do not want to simply boost the volume of the track, but may want to cut or boost certain frequencies to allow it to "sit" in the mix well.
2. Boost the frequency 3kHz by 3db's using the built-in equalizer in the software program you are using to edit the audio. This will usually make the vocal sound clear and give it a sharp sound. You may also want to cut that same frequency a bit on some of the more treble-heavy sounds such as cymbals and keyboards to help accentuate the vocal line without it sounding unnaturally loud. Accentuate or boost the mid-range frequencies between 500 and 700Hz to help the vocals stand out in the mix as well.
3. Compress the vocals using the built-in compressor included with your audio editing program. Start with a preset for vocals and make the necessary adjustments based on the vocalist. Bypass the compression first to get an idea of the peaks and valleys you hear in the vocals. Rapping is usually consistent and you may not need much compression. In some cases, compression can sound unnatural, so make sure you have enough to allow the vocal line to be heard, but not too much to ruin the track.
4. Adjust the compressor by starting with a gentle ratio of 2:1. The ratio is the amount of compression above the threshold dictated by the preset. In this case, the compression is two times reduction above that threshold. This will be very subtle, but also include a fast attack and release. The attack dictates how quickly the compression kicks in and the release is the time it takes for the compression to turn itself off. A quick attack and release will allow the rap vocals to sound strong and even.Increase the compression ratio until the meters for the track start to even out.
5. Mix the song using the desired compression and equalization and burn it to a CD or put it onto a flash drive. Take the track and listen to it in as many stereos as possible looking for any unnatural qualities in the vocals regarding either the EQ or the compression. Make notes and make the proper adjustments. It is often difficult to get it right the first time unless you are familiar with the way these effects work on a particular voice.
