Buying an external microphone is a common first step to improving audio quality for video. However, not all external camera mics make significant improvements in audio quality, especially considering that microphones struggle to capture sound from a distance. An article from Shure explains,
“The reality is that microphones do not reach out and grab the sound from a distance. They merely measure pressure variations right at the diaphragm itself. The microphone doesn’t “know” anything about what is happening at any distance from itself. For this reason, if you try to characterize a microphone’s “reach”, it’s almost completely dependent on the ambient acoustic conditions around the microphone.”
Some microphones employ directionality to decrease the sound entering from the sides and rear of the microphone. These typically have the advantage of decreasing the undesired sound entering the microphone by facing the null-point(s) of the microphone away from undesired sources. Unfortunately, the best microphones for capturing sound from a distance can be large and unwieldy, so camera-mounted mics strike a balance between audio quality and form factor.
While the right mic can improve audio quality for external camera microphones, there’s no substitute for getting closer to the sound source. For best results with any microphone, keep the subject within 3’ (1m) of the microphone and isolate the mic from loud, unwanted sound. If the subject requires more distance, either get the mic off-camera and closer to the subject, or place a lavaliere mic on the subject. Microphones have the physical limitations of acoustics and hardware, so if you’re getting poor audio results, getting closer can improve the sound quality.
A Primer on Microphone Polar Patterns
Built-in Camera Microphones
Most modern DSLR, mirrorless, and smartphones cameras come equipped with built-in microphones for mono or stereo audio recording. These mics are typically either omnidirectional or cardioid, and can work well for capturing sound in close proximity to the camera. Try speaking into your camera’s microphone while standing within 3’ (1m) in relatively quiet, indoor environment. The audio will likely sound clear and usable, especially directly in front of the lens.
Using an iPhone 11, Samsung Galaxy Note 10 or newer? These smartphones come equipped with “Audio Zoom” that artificially isolates the sound in the camera’s field-of-view from sounds off-camera when shooting video. These devices have microphone arrays and sophisticated DSP algorithms that can work better than external microphones in some cases.
Most entry-level external camera microphones have a cardioid polar pattern that captures sound from the front of the diaphragm, and attenuates sound from the rear (as seen in the diagram above). These unidirectional microphones capture the widest pattern from the front, and provide a deep null from the rear.
Using cardioid microphones on top of a camera result in difficulty capturing sound from a distance. They’re sensitive to the ambient noise of the environment, and typically sound best within 3 feet (1m) of the microphone. This makes them impractical for most filming situations, and rarely provide an improvement over a camera’s built-in microphones. Unfortunately, external camera-mounted cardioid mics provide very little benefit for audio capture, and we recommend avoiding them altogether. This said, cardioid microphones can be useful when mounted off-camera, in close proximity to the subject.
- Natural sound in quiet rooms with good acoustics
- Excellent off-axis rejection from the rear of the microphone
- Requires close proximity to the mic
- Offers little advantage over the camera’s built-in microphones
- Poorly suited for on-camera video use
Cardioid Microphone Variations – Supercardioid & Hypercardioid
Supercardioid and hypercardioid are modified cardioid patterns that reject more sound from the sides at the cost of reducing attenuation from the rear. These two polar patterns differ from a technical standpoint, such that supercardioids provide roughly equal attenuation from the sides and rear of the mic, whereas hypercardioids provide more attenuation from the sides at the expense of less attenuation from the rear.
For use as camera-mounted mics, these are typically preferable to cardioid mics as the added attenuation from the sides of the mic helps to better isolate sound originating from directly in front of the lens. It’s difficult to distinguish between the two patterns in real-world use, but hypercardioid mics offer a slight advantage with their increased rejection from the sides of the mic.
With the improved pickup from the rear of hypercardioid mics, they might seem like better options for scenarios wherein the person behind the camera occasionally speaks. However, the frequency-response of hypercardioid mics typically decreases at the rear of the mic, resulting in a tinny or muffled sound. Sound behind the mic will be slightly more audible than with a cardioid mic, but hypercardioids don’t offer a true bidirectional response.
- Moderately priced
- Typically small and lightweight
- Good balance between attenuation from the sides and rear of the mic
- Slight improvement over most built-in camera mics
- Can be more expensive than cardioid mics
- More sensitive to sound from the rear than cardioid
Shotgun, or rifle microphones are commonly used in video production and filmmaking for their ability to reject sound from the sides of the mic. As mentioned previously, shotgun mics have no better “reach” than other mics, but can offer better results in some situations. As an article from Sound On Sound points out, all shotgun mics use a common directional capsule with an “interference tube” that intercepts incoming off-axis, high-frequency sound. These mics offer some slight directionality over supercardioid and hypercardioid patterns, but off-axis attenuation decreases substantially at lower frequencies. This means that shotgun mics mostly block high and upper-midrange frequencies from the sides of the capsule.
The length of the microphone barrel makes a difference in how well the microphone blocks off-axis sound. Longer microphone barrels offer better off-axis “interference”, whereas short barrel shotgun mics offer little to no advantage over supercardioid and hypercardioid designs. In fact, the microphone element inside of short barrel shotgun mics can have more noise, since more sound pressure is required to reach the microphone element through the interference tube.
Shotgun microphones typically offer superior performance when mounted on camera compared to built-in camera mics, but we feel they aren’t worth the premium price over supercardioid or hypercardioid microphones. This said, many shotgun mics come with handy accessories, like shock mounts to reduce vibration noise, or a windscreen kit for use outdoors. The benefit of using these accessories can be worth the drawbacks of slightly increased noise and poor off-axis attenuation.
- Fairly lightweight
- Good off-axis rejection, esp. at high frequencies
- Preferable to built-in camera mics
- May come with useful accessories like a shock mounts and windscreen
- Can be expensive
- Can be long and unwieldy
- Short shotgun mics offer little benefit over supercardioid and hypercardioid mics
- Off-axis frequency response can be inconsistent
Windy environments necessitate the use of a windscreen, or material to shield the microphone from low-frequency wind noise. These are a necessity outdoors, and occasionally indoors near fans and strong HVAC systems. Greater amounts of wind require more material for shielding, and thus require the use of more dense materials like “dead cat” windscreens to block incoming wind noise. External microphones offer the advantage over built-in camera mics by allowing for the use of windscreens to block wind turbulence against the microphone.
More dense windscreen materials attenuate high-frequency sounds, and may result in a slight “muffled” audio quality when in use. A bulky windscreen may also interfere with camera operation, potentially obscuring the camera lens. This is why most manufacturers of external on-camera shotgun mics have shorter barrels, despite poor off-axis rejection.
Externally mounted camera mics can offer some benefit over built-in camera microphones, but still have limitations due to their size and difficulty capturing sound from a distance. When opting for an on-camera microphone, it’s best to choose a supercardioid or hypercardioid design, as these provide the best combination of size and directionality. Short shotgun mics offer little improvement over cardioid designs, and longer shotgun designs can be unwieldy and impractical to use when mounted on a camera.
External camera mics provide the option to use windscreens, making them more suitable for outdoor use than built-in camera mics. Windscreens block incoming low-frequency wind turbulence that can result in wind noise into the microphone. Choose a mic with a windscreen that won’t be so large as to block the lens or otherwise interfere with camera operation.
We hope this helps you narrow down your selection for choosing an external camera-mounted microphone. Keep in mind that getting closer to the sound source is one of the easiest ways to improve audio quality. If you can’t use a lavaliere or get the microphone off-camera, opt for good hypercardioid microphone to mount on-camera instead.
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