Compression Red Flags

Before I start, I should disclose that using solely visual clues to help you mix and master will never work out. You could have a waveform that looks similar to your favorite track but sounds like garbage because the compressor so dramatically treated it. What visual clues can do, however, is divulge the following process, which may exacerbate problems you may not be hearing on your system. All of these clues are geared toward those looking to use compression correctively in a non-creative way. If you're trying to create an effect or sound design with a compressor, this is not the article - try Trash Your Sound: Distortion.  

1) Crude Truncated Waveform

If your waveform looks like this after compression….

You probably have too much post-gain, or your attack time is too slow.

~ With Hard Digital Clipping

This is perhaps the most preventable of compression issues. Sometimes, you get the ratio and threshold just right, but you come in too hot with the gain, and sometimes, the input is hot, and your threshold isn't set low enough to soften it.  

What You Should Try Instead…

If there is clipping in the recording, Have the track re-recorded.

If the clipping is from your compressor, I recommend resetting the gain to 0 dB on your compressor, rendering the output, and looking at the compressed waveform.

It often helps to separate the compression step from the post-effect gain step. This way, you can see how much headroom you have and ensure the waveform is still healthy before boosting it. By looking at the compressed waveform, you know the effect of dynamic range processing. Rendering audio to a new track is a piece of cake in SoundBridge. Open the freeze dialogue, enable freeze to "new track," select the track, and hit OK. Notice how the lower waveform in the picture below looks much denser than the uncompressed and even has gain applied, yet it is not clipping.

Be careful. The higher the compression ratio, the more squashed the transients above the threshold will be, and the more added content there will be. On the other hand, if the ratio is too low, you may not have enough room to get the track to the master level you want. It is up to you and your ears to decide how much dynamic range you will sacrifice to make the track louder.

~ Cleaner kick at the cost of a higher noise floor.

Remember, when you turn up the compressed signal, you weaken the signal-to-noise ratio. Generally speaking, you don't want to have to do this. It is better to ask for a less dynamic mix than to squash all the loud stuff and compress the result upward.  

2) Spikes of Doom

If your waveform looks like this after compression…

Maybe you need some look-ahead to compensate for latency.

~ Sharp "popping" drums.

What You Should Try Instead…

Option 1 (ideal): To preserve the transient of the source, you should first try bringing down the level of the percussive sound and not compressing it at all. This way, the peaks come down in the mix but are not timbrally altered by the compressor.

Option 2: Try compressing the percussions individually instead of in a mix. If you choose this option, I would not recommend further compression on them - give them their signal chain or master bus.

Option 3: Try making some adjustments to the compressor. Your compressor will need a quick 1 ms attack to catch the percussions and perhaps some look-ahead time. Maybe something like 3 ms. I recommend soloing the sound in question and listening to it in isolation with compression. Find a balance between preserving the character of the sound and making it louder. Notice that the waveform in the image below removes those sharp transients you see in the image above, ensuring some needed headroom. This is a healthier waveform but not an ideal fix because it changes the character of the transients of percussive sounds.

~ Improved with a 5 ms look ahead.

3) Stuffed in a Tube

If your waveform looks like this after compression…

Your threshold is too low for the ratio, or your ratio is too high for the threshold.

~ Added content and drastic "pumping" due to over-compression

As you bring down a compressor's threshold, the effect of a high ratio is exaggerated. As you bring up the ratio, the effect of a low threshold is exaggerated. You may have gotten your dynamics flattened out but at the price of a lot of gain reduction and distortion. Bringing the gain back up will exacerbate all added content from the compression, severely weakening the signal-to-noise ratio. If you are in this predicament, you must return a step or two.  

What You Should Try Instead…

Option 1: Consider no compression.

Option 2: Go back to the compressor and try gradually increasing the threshold. This means instead of squashing the majority of the signal, you're only squashing the louder content. If this doesn't sound clean, try option 3.

Option 3 (ideal): Try using two compressors in serial instead - one to compress the softer content upward and another to compress the loud peaks downward. The image below shows how the waveform has transformed after each compression stage. Notice how the third waveform is less dynamic than the first two, has more headroom, and is not clipping.

~ Improved by using Serial Compression instead.

4) Big, Side-Ways Tornadoes

If your waveform looks like this after compression…

Your release time is probably too long.

~ Percussive sounds "swallowing" the rest of the arrangement.

It's not an issue of the compression amount or the threshold but rather an issue of how long the compressor is active. It squashes things you don't intend to crush or squash the sound too long.

What You Should Try Instead…

Option 1 (ideal): Ask yourself. "Do I want to make all this louder, or do I just want the loud stuff to be quieter?". If the latter is your answer, try using a limiter with a higher threshold and ratio instead of a compressor (they are separate units in SoundBridge). The release time can be a little longer, but it will only affect the top of the waveform.

Option 2: Shorten the release time. Then, listen carefully and estimate how long the sound(s) you wish to compress is(are) undesirably loud. Try tweaking the release parameter from that point. The image below is the same source with the same threshold and ratio - but a release of only 50 ms.

~ Improved by shortening the release time to 50 ms.