Advanced EQ techniques

EQ also can be used as a corrective measure. The techniques described in the preceding sections aimed to improve the overall sonic quality of your audio by focusing on what you wanted to be heard. You also can use EQ to remove extraneous noise that you don't want in the file.

Clearing up noise
If you recorded your audio in a noisy environment, you can use EQ to get rid of some of the worst noise. First, roll off all the low frequencies. You should do this regularly to all frequencies below 60Hz, because they're generally not reproduced by most systems. You can roll off more if you're dealing with serious noise. For example, traffic outside a busy city window will be audible as a steady low rumble, with the occasional siren or horn. If you roll off more of the bottom end, the sound of the traffic will be less audible.

Similarly, you can roll off high frequencies if you have noise problems such as air conditioning or tape hiss. In the preceding example, we boosted all frequencies above 5KHz to give the file some air; clearly, this is not something we'd want to do if we were in a noisy environment. Of course, we could have used the shelf to roll off all high frequencies above 8KHz or so and added a slight lift around 4–5KHz. Very little important voice information is in the range above 10KHz, so if you have noise problems, you can safely roll this off without any damage to the intelligibility of the audio.

Of course, in extreme situations, you can get pretty savage with EQ if necessary. For example, sometimes news reporters outside during a storm sound like they're talking through a telephone line. This is because the audio engineer at the station has rolled off all low frequencies and high frequencies, leaving just the mids.

Pops
Sometimes, a pop sneaks into your audio file, even if you're using a pop screen. If you zoom in to your audio file and look at the offending pop, you'll see that it's a very brief, very loud low frequency burst. You can highlight the offending word (or even syllable) and roll off the offending bass frequencies, as shown in Figure 1.


Figure 1: A pop is visible as a short, loud low-frequency burst, which can be fixed with EQ.

Experiment with different amounts of roll-off at different frequencies. You'll find that if you roll off too much, you get rid of the pop, but the result may sound unnatural. Find a good balance between removing as much of the offending pop as possible, while retaining the natural feel of the original.

Dealing with sibilants
Some people have a problem with sibilants, which are consonants like the letter "s" ("d" and "t" can also be a problem but usually nowhere near as much) that contain a burst of high-frequency information. This is audible as a whistling or, well, an "ess" sound. A little of this is natural, but too much is annoying. Some people actually whistle when they pronounce these consonants, which is an extreme version of the same problem. Because this is usually a very localized problem, it can be dealt with using EQ.

Sibilants usually are most prominent around 5KHz. Just like the preceding example where a word was highlighted and bass frequencies were rolled off to get rid of a pop, you can highlight a word and try to cut the offending frequency. Dealing with sibilants is more troublesome than popping, because our ears are very sensitive to high frequencies, and even if it's only a momentary change, our ears may notice that the sound has changed. Not only that, but if someone has trouble with sibilants, it usually manifests itself throughout the entire interview — and the letter "s" is very popular in the English language. In general, if you want to deal with sibilants, you should use a de-esser. That's a fancy term we audio engineers made up to describe a "frequency dependent, side chain controlled compressor." De-essers are explained in the compression section, which comes next.

EQ: A step-by-step example

This section steps you through the EQ process, with both graphic and parametric EQ. We'll assume that this is a male voice track that needs a little bit of sparkle. We're trying to do the following:

- Add a bit of warmth to the bottom end.

- Add a little clarity to the midrange.

- Give the vocal a bit of air, a little extra shimmer.

We're going to assume that you're using a software equalizer, though there's no reason that this couldn't be done using a hardware EQ. Also, the frequencies we're choosing in this example may not be the best frequencies for your audio, although they're probably a good place to start. Remember: Use your ears:

1. First, roll off the extreme low end. Chances are good (unless you have an extremely deep voice) that there is no information down here, except for possibly some room noise. Let's roll off everything below 60Hz.

On a graphic EQ, push down the faders below 60Hz. If you have more than one, start off gradually, rolling off about 3dB at 60Hz and then increasing the roll-off with each lower frequency.

On a parametric EQ, choose a high-pass filter at 60Hz and roll it all off. Shelving EQ has gradual roll-off built in.

2. Listen to your audio. You shouldn't hear much of a difference, if any. That's fine. You may hear a slight clearing up of the sound, and if so, that's even better.

3. Next, work on the midrange, because it's the most important. To give a voiceover a slight lift, you can boost the upper mids in the 2 – 4KHz range.

On a graphic EQ, pick a frequency in this range and boost it significantly, say 6-10dB. Preview your audio. Return that frequency to no gain, and try boosting the frequencies on either side, previewing each time. When you find the frequency that sounds best for your content, boost it 3dB and then boost the frequencies on either side 1.5dB, so there's a nice gentle lift. Preview the audio, and make sure it sounds good.

On a parametric EQ, choose a narrow Q and boost a frequency in the 2 – 4KHz range. Preview your audio. Try moving the frequency setting up and down, until you find the right frequency. Preview the audio each time you change the frequency. After you settle on a frequency, widen your Q to approximately 1.5. Boost 3dB, and give your audio one last preview to make sure you're doing the right thing.

4. Now listen to the low mids. The low mids are roughly where the sounds "er" and "uh" live. (If you've ever seen a sound check before a live gig, you'll hear the audio engineer making these sounds in the mics to check the EQ.) These frequencies give our ears information about the size of a room. You can often clear up a mix by cutting here, but be careful: You can make your audio sound too thin if you cut too much.

On a graphic EQ, you can experiment with cutting around 300Hz. You can do the same on a parametric EQ, with the added benefit that you can make the Q very narrow, to avoid thinning out your mix too much. Be sure to preview your audio to make sure you're making it sound better and not too thin.

5. If you're worried about the bottom end of your audio, particularly after cutting a little at 300Hz, you can add some warmth by boosting the bottom end. We rolled off the extreme low end earlier, but those frequencies are generally inaudible on most systems. To add audible bottom end, you need to boost in the 80 – 200Hz region. Where you boost depends on what (or who) you're EQing. The bottom end of male voices is usually around 100Hz; female voices are closer to 200Hz.

On a graphic EQ, you can find and push the frequency you're looking for. You may want to push the frequencies on either side slightly, as well. And the same goes for parametric; find the frequency, choose a fairly wide Q, and boost a bit. Preview your audio.

6. Finally, you need to decide if your audio needs any final sparkle. You can add this by boosting your high frequencies ever so slightly.

On a graphic EQ, start lifting at around 5KHz and boost the frequencies above 3dB. On a parametric EQ, select 5KHz for your shelving frequency and boost 3dB. Preview your audio. If you're happy with the sound, apply it! You may want to save this as a preset if this is a setting you think you'll be able to reuse.

Figures 1a and 1b show the results of all the preceding steps using graphic and parametric EQ. Your results may be slightly different; in fact, they should be, because you're listening to something different!




Figure 1: The results of the step-by-step example, illustrated on a) a graphic EQ and b) a parametric EQ.

EQ (Equalization)

EQ (Equalization)
Equalization, or EQ as it is commonly known, is adjusting the tonal quality of audio by turning up or down certain frequencies. Audio engineers use the terms boost for turning up and cut for turning down. Many of you are probably familiar with EQ via the bass and treble controls on your home or car stereos. In fact, you may have already fiddled with these knobs to adjust the sound; congratulations, you're an audio engineer. Using your ears as a guide, you adjusted the EQ until it sounded right to you. That's exactly what EQing is.

EQ is used for a number of reasons. Sometimes you may need to enhance the tone of your audio by boosting frequencies that make your audio sound more pleasant. You may need to boost these frequencies to make up for a deficiency in your mic or because your voice sounded different one day due to a cold or a late night. On the other hand, you may want to cut frequencies that aren't helping the sound of your audio. This can also be due to a deficiency in your signal chain or to get rid of something unpleasant, like an excessively nasal sound or too much bottom end.

How to use EQ
At the end of the day, it's all about making your audio sound better. You want your podcasts to sound bright and full, not dull and thin. You may notice that the terms used to describe the effects of EQ are very subjective. Audio engineers regularly use terms like "presence," "sparkle," "warmth," and "air." Believe it or not, these terms aren't that subjective; they're actually ways of referring to certain parts of the frequency spectrum — where exactly in the spectrum is subject to debate, but in the next section we provide you with a table of frequency ranges, along with common terms used to describe the frequencies in each range. The first thing to do, however, is to listen to your audio critically and ask yourself a few questions. The following questions start at the bottom of the frequency range, and work up from there, but you can think about them in any order you like:

- Is it "warm" enough? Is there enough low frequency information? Be careful here, because even good studio monitors have a hard time reproducing the lowest audible frequencies.

- What about the midrange? Are the voices clear and understandable? Or is the sound too harsh?

- How about the high frequencies? Does the audio sound dull? Or do you have the opposite problem — too much high frequency information?

If you're unsure about the answer to any of these questions, do what other audio engineers do — use something else as a reference. For example, you could listen to a radio program that is similar to yours, and do what we call an A/B comparison. Listen to the radio program for ten seconds, listening in particular to the low frequencies. Then flip back your podcast, and compare. Does yours have less? More? Flip back and listen to the middle frequencies, and compare. Finally, listen to the high frequencies. This should give you an indication of whether your podcast is up to scratch, and if it isn't, what you may need to add (or cut) to make your podcast sound better. The trick is to find the right frequencies.

Podcast: Signal processors

Audio production techniques that you can use to optimize your podcast. These can be done using either hardware or software. Software is convenient because you can use presets or create customized settings for your podcast that you can use every week. Even more useful is the ability to "undo." However, sometimes hardware processing is handy. You can't beat the feel of real knobs, and who wouldn't like more flashing lights in his studio? A couple of hardware processors are shown in Figure 1.


Figure 1: Signal processing units: Presonus Comp16, EQ3B

Equalization (EQ) units
Equalization is a process whereby tone is altered by boosting (turning up) or attenuating (turning down) certain frequencies. The bass and treble knobs on your car stereo apply EQ. Most mixing desks include simple EQ, but you may want finer control of your tone at times. In this case, you'd buy an external EQ unit. You also can use EQ units to fight feedback problems (refer to the "Feedback: What It Is and How to Avoid It" sidebar).

Compressor
Audio compressors help control your audio levels. Compressors turn audio levels down when they cross a certain threshold. They're incredibly useful because they protect your equipment from distortion due to abrupt level changes — for example, if one of your guests suddenly starts yelling. You can place a compressor between your mixing desk and your audio interface as a protective measure or compress your input channels individually.

Effects units
Effects units enable you to add special effects to your podcast, like echo and reverb. Effects are often used in music production to make the band sound like they're playing in a large hall or club. For most podcast material, this simply isn't appropriate. If you listen to the radio carefully, you'll notice that special effects are used sparingly, and even then only on the "bumpers" (the show announcements) or on advertisements.

Audio interfaces
At some point, your analog audio signal must make the transition between the analog and digital worlds. This can be done at various points in your signal chain. Once upon a time, the only way to get sound into your computer was via a soundcard, but that is no longer the case. Audio interfaces can connect via USB and FireWire, mixing desks come with built-in audio interfaces, and you can even buy USB mics.

Soundcards
Virtually every computer sold these days comes with some sort of audio interface. Usually, there's a headphone and/or speaker output, a microphone input, and a line level input if you're lucky. The problem is that these soundcards are usually built with really cheap components and are low quality. Microphone inputs on soundcards tend to be very noisy. They're very vulnerable to electrical interference (of which there's plenty inside a computer). In general, you should avoid using the mic input on a soundcard.

This doesn't mean that you can't produce a podcast using whatever soundcard you're stuck with. Hey, the idea is to get podcasting as quickly as possible, right? If you must use the soundcard that came with your hand-me-down computer, and if you must use the microphone input, go right ahead. Just remember that when you decide it's time to improve the audio quality, the soundcard is probably the place to start.

Plenty of good soundcards are available today. You should look for a soundcard that uses professional 1/4″ or XLR connectors, because they're far more reliable and resistant to noise. Many soundcards these days come with a breakout box that you can place on your desk or a shelf, so you don't have to crawl behind your computer every time you want to plug something in. Check out the example in Figure 2.


Figure 3: Soundcard with breakout box: M-Audio Delta 44

External audio interfaces
Another way to get digital audio into your computer is to use an external audio interface. This type of stand-alone unit connects to your computer via USB or FireWire. Until recently, only a few of these were available, but now you have lots to choose from. One nice thing is that most of these units come bundled with tons of great recording tools, so if you don't have an audio editor, you might consider picking up an external audio interface just to get the software!

Like soundcards, external audio interfaces come in many shapes and sizes and have different features, such as number of inputs and so on, like the ones shown in Figure 5.14. One thing to consider is power; most of these units run off the power supplied by the USB or FireWire bus, but to get power on a FireWire cable, you need the larger six-pin cable. Some laptops come equipped only with the smaller four-pin FireWire input, so you'll have to supply external power if you're using a FireWire interface. For the ultimate in portability, you may want to go with a USB version.


Figure 4: External audio interface: M-Audio Mobile Pre (USB), PreSonus Firebox (FireWire).

Recording devices
You have a number of options for recording. The most obvious is to record directly to your hard drive. However, this may not be an option if you're recording on location, or if you don't want to lug your computer around with you everywhere you go. Of course, these days, people bring their laptops with them everywhere, but if you don't want to do that, this section discusses other options for recording your podcast.

You can record in many different formats. Some, like the cassette, have been around for ages, but are still entirely useful. Others, like tapeless recording, are relatively new. Tapeless recording is of particular interest to podcasters, because you can transfer the files from your recorder to the computer digitally and much faster than real-time transfers.

Cassette
Cassettes were initially developed as a dictation format and never designed to be high quality. But they caught on like wildfire, so manufacturers improved the tape quality and the electronics, and they even added noise reduction systems like Dolby. If you have a decent cassette deck lying around, you can use it, but be sure to buy high-quality chrome cassette tapes and set your record levels high so you don't hear tape hiss. Of course, you can always use studio trickery later on to get rid of (or at least reduce) tape hiss.

DAT
Digital Audio Tape, or DAT, appeared in the mid-1980s as a high-quality studio format, but found its way into the consumer market. Although it has largely disappeared in the past ten years, plenty of serviceable DAT machines are still out there, and they're very high quality.

MiniDisc
Sony has been trying to convince the world that MiniDisc is a great format, but few people have listened. MiniDisc just never seems to go away, no matter how poorly it sells. This is partly due to the fact that MiniDisc units use ATRAC compression on the audio signal, which is acceptable for spoken word content, but not really acceptable for recording music masters. As a portable podcast recorder, a MiniDisc unit can be quite useful, especially because you can find them on craigslist for under $50 and MiniDisc blank discs are cheap.

MP3 recorders
A handful of MP3 players include record functionality. Most of these units do not have external mic inputs. A few have a line input that you can record from, but this means having some sort of mixing desk for the mic pre-amps and feeding the line level output into your portable MP3 player — not exactly a compact setup. Of course, you can use the built-in mic these units tend to include. If you're in a quiet location, it's probably fine. But don't expect broadcast quality.

New tapeless options
If you want the latest and greatest, look no further. Several manufacturers have released high-quality tapeless recording options in the last year. You can see some examples in Figure 5.15. These units record to compact Flash memory cards, which you can pop out and put into a USB card reader connected to your computer, or you can connect the unit to your computer using a USB cable. This allows you to transfer files much faster than real-time transfers; the transfer time depends on the type of file you recorded.



Figure 5: The M-Audio MicroTrack 24/96, a portable recorder that records to Flash cards or microdrives

These tapeless units generally offer uncompressed recording in the WAV format, as well as MP3 recording at a variety of bit rates. Most come with built-in microphones, but for highest quality you'll want to use your own mics, of course. Some units offer XLR connectors, some 1/4″ or 1/8″. As of the writing, models are available from four manufacturers, but we're sure you'll have many more choices by the time you read this.