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We all know that great audio is critical to a successful production. Next we'll show you some tools for sweetening your mix and and even correcting those inevitable audiosyncracies. Soon you'll be using Audio Effects and Filters such as the EQ, Lowpass, Highpass and Notch filters, as well as compressors, limiters, and reverb, to have your audio sounding its absolute best.
Try as we might, seldom are we able to capture perfect audio. Often we'll discover hisses and hums from fans, refrigerators and other sources we either didn't notice or found impossible to avoid. Sometimes we'll want to further improve our mix by bringing the highs and lows closer together for better balance, adjusting gain and reducing peaking. In this segment we'll use Adobe's Premiere Pro CS5 editing program to demonstrate some useful tools for achieving great results. Most editing programs will have similar tools, and audio specific programs, such as Adobe's Audition and Soundbooth, will have even more options.
The EQ effect provides a great deal of control over your audio, allowing you to sweeten - or improve - its sound, by enhancing frequencies you want to hear more of, reduce those you'd prefer in the background or even eliminate unwanted sounds altogether. In the Effects window search bar type eq. Three folders open - 5.1, Stereo, and Mono - each containing the EQ effect. Drag EQ from the appropriate folder and drop it onto your audio clip. In the Effect Controls window twirl down EQ, then open Custom Setup. Click the frequency bands you wish to adjust: Low, Mid1, Mid2, Mid3, High or all of them. Once selected, band handles appear on the line in the frequency window. At the bottom of the Effect Controls window locate the Toggle looping audio playback button. Click it, then click the Play only the audio for this clip button to its left. While playing the clip, drag the handles left or right to affect different frequencies and up or down to increase or decrease gain. Dragging the two smaller markers on either side of the larger one broadens or narrows the frequency range affected. This same effect is achieved using the Q dial control on the graphic interface below. The Cut check boxes are used to eliminate low-end rumble and high-end hiss, and the Output slider compensates for changes in the overall gain. Toggle the effect on and off using the Bypass checkbox. To sweeten a voice track you might boost the higher frequencies to make the esses and tees cleaner, then enhance the lower frequencies for more depth. To correct an offensive sound with a known frequency, such as 60Hz electrical noise, enable the appropriate band, dial in the frequency, narrow its range and drop the gain til it disappears. If the frequency is unknown then a little trial and error will be in order.
A low-pass filter allows frequencies lower than the cutoff value to pass through while cutting off higher frequencies and is useful for reducing an annoying hiss. Locate the Lowpass filter in the Effects window and drag it onto the clip. Twirl the effect open, and while the audio clip loops, adjust the cutoff values until the hiss goes away. Click the Bypass check box to toggle the effect on and off so you can hear the difference.
A high-pass filter allows frequencies higher than the cutoff value to pass through, while cutting off lower frequencies, and is used to get rid of low frequency hum. Locate and apply the Highpass filter. This time, frequencies below the cutoff value will be affected. Make adjustments while looping the audio until you reach the desired result.
A notch filter passes most frequencies while reducing those within a specific range to very low levels and is oftentimes used with noises of a known frequency, such as electrical hum. Locate Notch in the Effects window and drop it onto your clip. If the frequency is known, type it into the Center value. If it isn't, then loop the clip, while adjusting the Center values until the correct frequency is found. Use the Q value to narrow or broaden the frequency range as needed.
A compressor is used to soften your audio's loud parts while boosting the softer portions to create a more even sound. Locate the Dynamics effect and apply it to your clip. With Custom Setup open, check Compressor and begin by setting Ratio to around 2-1/2 to 3 and Threshold between -8 and -14. This is a good starting point and you can fine tune from there. Loop the clip while adjusting Threshold to alter the level at which processing begins and Ratio to control the amount of compression that is applied. Be sure to avoid over compressing. When your volume is at -6 decibels with peaks below zero it'll be just about right.
A limiter is used to prevent clipping, the distortion that occurs when audio levels reach into the red. Within the Dynamics effect click the Limiter checkbox. Set the Threshold to -0.20 dB. Anything higher will automatically be reduced down to -0.20 dB and will prevent the signal from clipping.
Reverb is used to simulate the ambiance within a room, adding dimensionality and warmth to your audio. Apply the Reverb effect to your audio and twirl open Custom Setup. While looping, drag the white squares in the graphic or adjust the dial controls until you find just the right sound. Pre Delay adjusts the distance a sound travels, Absorption determines how much the sound is absorbed, size reflects the size of the room and Lo Damp is used to prevent rumbling while Hi Damp softens the overall effect. Mix determines the amount of reverb that is applied.
For supremely satisfying audio, learning to use these Audio Effects and Filters will certainly be a worthwhile investment of your time. Apply the tools and techniques we've shown you here and your next project will have your audience on the edge of their seats hanging on every decibel!