Audio for Video: Part 1 - The Basics

By: Joshua Martin

As many FlickerTube.Com readers are filmmakers with various degrees of experience and budgets, I am now producing an accompanying series of audio for video tutorials to accompany the previously published filmmaking tutorials. These tutorials will describe the essential equipment and steps required for creating professional sounding results with an inexpensive and moderate budget scheme - independent of your musical talents - using your home computer system.

In Part 1, I cover what you need to know to understand the basic audio equipment necessary for recording. These details are also very valuable for many other purchases you’ll make, from stereo equipment to headphones to other sound recording gear.

Microphones - Microphone (mic) choice is, often times, based on another’s knowledge or experience, like friend recommendations, a good editorial, or magazine review. But how can you really determine how a microphone will perform without ever using it? You can’t entirely, but you can always begin with the specifications to help you determine what model to look at closer as well as to interpret and understand what the magazines are talking about. However, in the end it is your ears that should make the final decision; nothing else.

The most popular specification in the audio industry is frequency response, displayed in Hertz (Hz). Frequencies represent the travel of sound waves - a wave travelling 220 times per second produces the pitch “A” just below middle C. As a reference, the maximum range of human hearing is from 20 Hz to 20 kHz (20,000 Hz). This is the range of sounds, from low to high, that the microphone can record.

However, this is only a small part of what the frequency response is all about. If you look at Figure 1, you’ll notice that the two dark, bumpy lines are not perfectly straight, or “flat.” What this graph shows us is how the mic performs, or responds, at each frequency. The frequencies are listed from lowest pitch to highest along the horizontal X-axis. The perceived volume changes, measured in decibels (dB), are along the vertical Y-axis. Keep in mind that a dB is a relative measurement from 0. The top wavy line is the measurement taken when facing the microphone head-on: 0 degrees. The bottom line is the response from behind the microphone, or 180 degrees. This is important, as much of the character of the room you are recording in will be captured from the rear of the mic. Therefore, if we were recording a piano with the mic that is represented in this graph, the lower notes, around 150Hz and below would be quieter than those around middle C. As we move up the keyboard we’d find that the higher notes would be a little louder. Also, if we were recording in a small room, we might find that some reverb reflections from surrounding walls on the higher notes would be much more obvious, and possibly interfere with the direct sound from the piano, then the lower notes. If it were in a larger hall, however, this boost might create a nice air-like quality.

So, what does all of this frequency response stuff mean? How do I know what to pick? The frequency response curve is what defines the microphone. It’s character; it’s personality. It all depends on what the microphone is going to be used for. Keep in mind that it’s not just what range the mic can record, but how it performs in that range. There is a mic out there for each different job, but no mic for every job. For example, you’ll find that many radio DJs like to use an Electro-Voice RE20 because it has great response in the lower frequencies and good rejection on the sides and back, resulting in a deeper, richer voice and performs well when spoken into at a close range. The AKG D112 is a popular kick drum and bass guitar mic since it not only performs well at very low frequencies, but it also has a narrow peak around 4,000 Hz which provides some extra “air”, bite, or snap to the sound. Perfect for slap bass. If you’re going to be recording classical or jazz music or anything that you want to sound exactly as you hear it, you’d want a mic with a very flat response. One that is as true to life as possible.

There is yet another specification to be aware of: SPL or Sound Pressure Level. This indicates how loud the source of your recording can be. You do not want to take a low-rated (under 100) SPL mic and use it on a snare drum or guitar amp. Not only will you get a lot of distortion on your recording, but you may also damage the microphone. Fortunately, some microphones provide a “pad” switch to increase the SPL handling of the mic.

Another variation on the frequency response is the polar response. The polar graph in Figure 2 represents the measured frequency response around the microphone. Just as Figure 1 showed us the 0 and 180-degree responses, this shows the full view. Microphones are made in various polar patterns, and you can select between patterns on some more expensive mics. Figure 2 displays a cardioid (sometimes called “unidirectional”) pattern. This is a very common pattern and is especially useful in live or noisy situations as most frequencies are only captured at the front and sides of the mic and the rear is cancelled out. On the polar opposite end of the spectrum (sorry for the pun) there are omnidirectional microphones which allow recording from all sides of the microphone. In between there is the figure 8 pattern, which has side rejection but records from the front and back. All of these patterns play a factor in how the microphone is used and ultimately sounds.

Microphone types: There are 3 main types of mics, based on their construction, that perform differently: dynamic, condenser/capacitor, and ribbon.

Most drum and live vocal mics, like the popular $99 Shure SM58 (“SM” is short for Stage Mic), are dynamics. Without getting into the details of their construction, dynamics are great live mics as they can really take a beating. Watch Mick Jagger or Steven Tyler thrash their mics around…I don’t think I’d put a $3000 Neumann up there! Dynamics also provide a decent, reliable sound and are used on many instruments, particularly for rock and pop music. One drawback from the dynamic mic is that it isn’t particularly sensitive to subtle changes or very detail-oriented music or fieldwork.

This is where the condenser comes in. The condenser mic is the most versatile type of mic, in my opinion. You can take, for example, a large diaphragm (the vibrating membrane, ranging from about ½” to 1.5”) condenser like the inexpensive ($350) Audio Technica 4033 and place it on a guitar amp and it will sound great. Put it on a male vocal, and you’ll be happy. Up close on the 12^th fret of an acoustic guitar and you’ll hear all the nuances of the string slides, wood, and pick or fingers. Get two of them and record a choir, quartet, or piano. One thing with condensers, however, is that most require phantom power. This is normally a switch found on your mixer that provides power to the diaphragm to polarize it. Whenever you press this switch make sure your volumes on headphones and speakers are down! If you don’t have a phantom power switch you can purchase a phantom power supply for around $35.

And the least versatile and least used mic type is the ribbon mic. If you ever come across one of these, be extremely careful as it has the lowest SPL handling of them all. Engineers have been known to cover these with a bag before moving them as the wind pressure as you move might break the diaphragm. This “drawback,” however, also makes it the most sensitive and natural sounding mic type. Fine ribbon mics may be used in classical music for a truly detailed reproduction.

Mixers - They do exactly as the name implies. Just like you use a mixer or blender to combine different ingredients in a recipe, an audio mixer allows multiple sources to be input, manipulated, and combined. The mixer is divided into 3 main sections. The input and output jacks, channel strips, and master controls. A classic industry workhorse example is the Mackie 1202-VLZ Pro.

On the input and output side of a mixer you may find three different jacks. A 3-pin XLR/microphone level jack, a ¼” TRS/instrument/line level jack, or red and white RCA/radio/stereo jacks. See for an example. XLR-style jacks are the professional standard for microphone input as well as for connecting your mixer to an amplifier/monitor speaker setup. The XLR jack runs at a lower level than the ¼” “line level” jack. Because of this you will find a small “trim” or Pre-amp knob to increase the level of your microphone input. The ¼” jack is mainly used for instrument I/O (input and output) such as guitars, keyboards, drum machines, and effects units. You’ll also see Insert jacks that are also ¼”. These allow you to place an effect unit like a compressor in the middle of the audio chain by using a single ¼” TRS (Tip/Ring/Sleeve) cable.

The vast rows of knobs, or the channel strips, really aren’t that confusing once you realize that many are duplicated for each vertical channel. Each channel is a different input. For example, channel 1 could be a lead vocal, channel 2 could be a bass guitar, and so on.

Most channel strips are arranged as the audio signal travels through the board. Beginning at the input, then to the pre-amp as the top knob (mic inputs only). Here you will also hopefully find a phantom power switch. If not, it may be located on the back of the mixer as some smaller mixers have a global phantom power switch. If you are using a condenser mic that requires phantom power, make sure that all of your levels are down before switching it on. You, and your speakers, will not appreciate that noise.

Below the trim knob you’ll find Auxiliary (aux) sends. This allows you to send signal to an effects unit for reverberation or other effects such as chorus, distortion, and delay. The output of the processor is then connected to the Aux Returns and controlled by the knobs in the master control section on the right.

Next is a different section of knobs that may vary in quantity from one mixing board to another. These are for equalization, otherwise known as “EQ”. This advanced form of controlling bass and treble, like those found on your car and home stereos, allows you to tailor the sound of each individual voice or instrument to your liking. As a rule of thumb, we try to attenuate rather than boost EQ settings, however, with our limited controls (either 2 or 3 knobs) a nice way to add a little clarity to vocals is to boost the 2.5k frequency by 2-3dBs. On some mixers, like the Mackie 1202, you’ll also find a quick switch to cut off everything below 75 Hz at the input near the trim knob. This is great for rejecting any unwanted low frequency noise on material that doesn’t extend that far down, like some voiceovers.

Below the EQ section is the PAN knob. This controls the placement of the instrument in the stereo field: between the left and right speakers. For voiceovers and single instruments you’ll want to leave them panned to the center.

Below the Pan knob is the gain/level/volume section. Here you’ll see the Mute button, which does exactly as it says…most of the time. In the case of the Mackie series, it also provides an additional, very useful function. It sends all muted channels to another output, known as the ALT 3-4 bus. This allows you many options. I often use it to send only certain channels to my computer if I need to monitor other channels as well. You’ll also find the Solo button that automatically mutes all other channels that are not soloed so you can accurately set the correct level for that channel. And of course, you’ll also see the nice big Gain knob, or on larger mixers a big slider known as a “fader.” Faders are great for making smooth and fast volume transitions. The knobs will work fine for us, though, since we’ll be making our transitions inside the computer in the next tutorial.

Last in the audio chain is the master controls section. Here you choose where to route the signal, what to listen to, and control and view the levels of the overall mix or soloed tracks. You’ll also find the controls for the Auxiliary returns and headphone volume here as well.

There you have it. A general overview of the basic tools required for recording music: microphones and mixers. There are many other pieces of gear that will become necessary as you search for your perfect sound. However, a lot of this gear is being replaced by computer software. We’ll take a look at that in another tutorial! Now, don’t know what to buy? Here are some of my recommendations:

For The Inexpensive Studio:

To begin recording voiceovers or live instruments, a good place to start is at Radio Shack. Here you can get a decent mic based on the more expensive and highly acclaimed Shure SM58, for about $40. This mic will be perfect for voiceovers and electric guitars, and sufficient for any other acoustic instrument. While you’re at Radio Shack, you’ll also want to buy a mic cable to either plug the mic into your computer or into a mixer.

If you are going to go directly into your computer (if you only plan on recording one voice or instrument at a time), you’ll need an XLR to ¼” cable and either a 1/8” mini plug adapter or RCA (consumer stereo) style adapter depending on your computer’s sound card. 1/8” is typical. Your new sound files should play back through your normal setup for listening to files on your computer. If you’re still using the built-in speakers on your computer or monitor, though, you may also want to pick up a computer speaker setup from Altec Lansing, Cambridge Soundworks, Monsoon, or Polk Audio.

If you are going to use a mixer, get some microphone cables (XLR to XLR) to connect your mic(s) to your mixer, two ¼” cables, and two adapters: a ¼” “Y” adapter which will combine the two cables into one, and a ¼” to 1/8” adapter so you can plug the “Y” adapter into your computer’s soundcard. If your computer has red and white RCA inputs, just get two ¼” to RCA cables. And if you’re still using the built-in speakers on your computer or monitor, you may also want to pick up a computer speaker setup from Altec Lansing, Cambridge Soundworks, Monsoon, or Polk Audio.

As for mixers, there are a few small, inexpensive ones that are really worth keeping. You could get one from Radio Shack, but you probably wouldn’t want to keep it forever as they don’t provide the expandability and features that you’ll learn to use (and crave) in time. So, instead, pick up a small Behringer MX602 ($89) from your local music retailer, from the online catalogs at Mars Music, Sweetwater Sound, Musician’s Friend, and American Musical Supply or check out the used classifieds at Harmony Central, Telesis, Digibid, or Ebay.

For The Moderate Studio:

Swing by your local music retailer to check out a few mics. I’d recommend a few of the industry standard Shure SM58 (approx. $99) for doing voiceovers and basic recording. If you’re interested in having an even better mic for just a little more, check out the CAD Equitek 100 for about $225.

If you are going to record more than one instrument or voice at a time, you’ll want a mixer. You just can’t go wrong with the immensely popular Mackie line and the 1202-VLZ Pro ($375) mentioned above is ideal. Older variations of the 1202 are easily found in the online auctions and classifieds listed below, but I’d stick to either the 1202-VLZ or the VLZ Pro. You may want to check out the Behringer MX802 ($129) or Spirit Folio Notepad ($169) mixers as well.

Pick up some microphone cables (XLR to XLR) to connect your mics to your mixer. To run the sound in to your computer, get two ¼” cables, and two adapters: a ¼” “Y” adapter which will combine the two cables into one, and a ¼” to 1/8” adapter so you can plug the “Y” adapter into your computer’s soundcard. If your computer has red and white RCA inputs, just get two ¼” to RCA cables. Plug the ¼” cables into the Control Room, Alt 3-4, or sub outs of your mixer.

Depending on your current setup, you may also want to run the output of the computer back into your mixer for additional mixing or straight into a stereo or set of powered “active” audio monitors such as those from Event, Yamaha, and Tannoy. To do this, just get another set of the cables that you got for your input: either the two RCA to RCA (for stereos) or ¼” (for monitors) cables, or the two ¼” cables and two adapters.

All of these products can be found at your local music retailer, from the online catalogs at Mars Music, Sweetwater Sound, Musician’s Friend, and American Musical Supply or check out the used classifieds and auctions at Harmony Central, Telesis, Digibid, or Ebay.

Wrap Up

As always, these combinations are merely examples and may be combined and altered to any degree. Please feel free to contact Josh at synthcomposer@excite.com with any questions, suggestions, or comments. Thanks for reading, good luck, and keep an eye out for the Audio for Video Tutorial: Part 2 - Voiceovers. Enjoy FlickerTube.Com!