A song I co-wrote and produced a few years ago finally got a music video made, and I even have a little cameo. The track was featured on the TV show Scrubs in season 8, on the episode “My New Role.”
A “pass” filter affects all energy above or below the target frequency, often referred to as the “cut-off frequency,” by removing that frequency content in a continuously decreasing downward slope. Pass filters are extremely valuable tools in mixing because they allow us to”bracket” the frequency energy of a given signal in the mix. We can use hi-pass filters to remove low-frequency mud or rumble from the recording process, or lo-pass filters to shave off hi-frequency content, pulling the signal back in the mix.
While most intermediate mixers are familiar with using hi-pass filters to remove mud and clear out unwanted frequency content in the low-end of a mix, many are unaware at how valuable low pass filters can be at smoothing out your mix’s frequency response and creating clarity and contrast amongst tracks. Unlike an analog mixer or analog tape, a DAW’s mixer is 100% frequency linear in it’s summing process, meaning that no frequencies are altered or “soaked up in the circuitry” during the summing process. Combine this with the fact that many modern virtual instruments and loop collections have an insane amount of high frequency extension (have you heard some of the “paint peeling” top end of plug-in synth presets lately?) and a mix can gather a boat load of fatiguing top end very quickly.
Aside from creating context (or lack there of) issues between the focal tracks in a mix (e.g. if everything has a ton of top end, the mix can lack a sense of depth of focus on the elements that you want to have pop out), I find that this build up of ultra high frequency content tends to do a few nasty things. First, all those high frequencies, if left un-checked, ram into the D/A’s anti aliasing filter all at the same time, and depending the quality of your D/A converter, can result in a nasty haze in the top end that muddles the stereo image and becomes very fatiguing to listen to over time. Second, and most important for a lot of the commercial work I am doing, I find that feeding a mix with way too much un-checked top end into mp3 (or any other compression) algorithms tends to force the algorithm to sacrifice important mid band bits in an attempt to retain a top end you can barely hear. In other words, mixes that aren’t insanely bright will tend to fair better under heavy audio compression.
Now I am not saying go and filter every track in your mix down to 10K, but I do find that subtle lo-pass filtering at very high frequencies with transparent EQ filters (e.g. filtering 6dB/oct at 12K, 15K, 20K, etc on certain non-focal tracks) can help give me a more analog feel and ensure that my mix sounds better when run through youtube’s compression algorithm 50 times.
To learn more about hi and low pass filters, check out this free clip from my Foundations of Audio: EQ and Filters course or watch the whole course at here at lynda.com
This entry was written by Articles, Audio and Video, MixTips, News, video and tagged EQ, equalization, mixing, producing, recording, song writing. Leave a comment or view the discussion at the permalink and follow any comments with the RSS feed for this post.
As humans, we have tons of built in “thresholds” surrounding all of our senses. What do you do when the shower gets too hot? As the temperature rises, it eventually gets to the point that your nerves tell your brain “ouch” and your brain tells you “too hot!” and you turn down the hot water. That point of “too hot,” be it 110 degrees or 120 degrees, is your skin’s personal threshold for water temperature. In the case of a compressor, the threshold control defines the point at which the compressor will begin to alter the dynamics of the signal, or compress. If the signal breaches the threshold or gets “too loud,” the compressor reacts by compressing or “turning down” the level of the output, just like you turning down the water temperature in the shower. In other words, It’s the threshold control that tells the compressor when to compress and when to leave the signal alone.
All dynamic processors work on the simple principle of a defined action resulting in a prescribed reaction. Think of it as an “if..then” statement of sorts; if the incoming signal level reaches “X” or higher, the processor will react in “Y” way, if the signal remains below X then do nothing. The threshold control in a dynamic processor allows us to define the reaction point, or the “if” part of the statement, setting the level at which the processor reacts, sometimes by reducing (compressing) or increasing (expanding) the level of the output.
I know what you’re thinking, you’ve seen that threshold control just sitting there, but the presets you pick automatically set for you, so what’s the big deal? Indeed, most compressor plug-in presets include a preset threshold value, and while it might be tempting to use that level, it is very important to understand that the preset threshold may not be affective for your specific compression task. If the threshold is set too deep, it might over compress the signal, removing all the dynamics. If the threshold is set too light, the compressor might not engage at all. Of course, sometimes you get lucky and everything works out, but remember, the preset has no way of knowing what your input level looks like or how much compression your signal needs. Until we have intelligent processors that can adjust their threshold automatically to accommodate the input signal, you will need to adjust the threshold control manually. Even if the processor could detect and adjust the threshold automatically based on the input signal, the preset couldn’t know how much compression you needed or desired, just like no one else would know just how hot you like your showers on any given day.
Ultimately, whether you set up your dynamic processors from scratch or from a preset, it is imperative that you understand and use the the threshold control to achieve the desired amount of processing. If you want to learn more and see some cool animations, watch the following free clip on understanding threshold from my new course lynda.com, Foundations of Audio: Compression and Dynamic Processing. Be sure to check out the entire course for more tips on using threshold and other compression controls.
This entry was written by Articles, Audio and Video, MixTips, News, video and tagged compression, limiters, mixing, producing, recording. Leave a comment or view the discussion at the permalink and follow any comments with the RSS feed for this post.