🎤 Bi-Directional Mics: Pick the RIGHT One! [Guide]

Understanding recording patterns is essential, and bi directional microphones offer a unique solution for capturing sound from both the front and rear. The figure-8 pattern, a defining characteristic of these mics, makes them ideal for interviews, podcasting with guests, or recording musical duets. Consider companies like Shure, known for their quality audio equipment, when exploring bi directional microphones. This guide will help you navigate the world of bi directional microphones, even if you’re just starting out. The use case for **bi directional microphones** often involves a recording studio, so keep the specific environment you plan to use them in mind as we walk through the core concepts you need to know.

Bi-directional microphones, often overlooked in favor of their cardioid and omnidirectional cousins, possess a unique sonic signature and set of characteristics that make them invaluable tools for specific recording applications. They capture sound from the front and back of the microphone capsule while rejecting sound from the sides, a pattern visualized as a figure-8. This distinct polar pattern opens up creative possibilities for capturing nuanced performances, achieving natural stereo recordings, and even isolating sound sources in challenging acoustic environments.

What is a Bi-Directional Microphone?

A bi-directional microphone is defined by its sensitivity to sound coming from two opposite directions: directly in front of the microphone and directly behind it. It picks up these sound sources with equal gain. Sound arriving from the sides (90 degrees off-axis) is largely rejected.

The key characteristics of these microphones stem from this focused sensitivity:

• Figure-8 polar pattern: The defining visual representation of its sound capture.
• High side rejection: Excellent at minimizing unwanted noise from the sides.
• Proximity effect: A noticeable increase in bass response as the sound source gets closer.

The Alluring Figure-8 Polar Pattern

The figure-8 polar pattern isn’t just a technical specification; it’s the key to unlocking the potential of bi-directional microphones. Understanding its nuances is crucial for effective use.

Unlike cardioid microphones that primarily focus on sound in front, or omnidirectional microphones that capture sound from all directions, the figure-8 pattern creates a specific zone of sensitivity. This zone allows for controlled sound capture, making it ideal for:

• Duets and interviews: Capturing two voices facing each other with minimal bleed.
• Stereo recording techniques: Creating spacious and natural stereo images.
• Acoustic treatment workaround: Minimizing room reflections by focusing on the direct sound and rejecting side reflections.

Why Choose Bi-Directional?

Why would you choose a bi-directional microphone over the more common cardioid or omnidirectional options? The answer lies in its specialized capabilities. While not a universal solution, the bi-directional microphone excels in specific situations where its unique characteristics offer distinct advantages.

Consider these scenarios:

• Isolating sound sources: The side rejection helps to minimize unwanted sounds and focus on the desired sources directly in front and behind the mic. This can be useful in live recordings or untreated spaces.
• Capturing ambience and direct sound: Bi-directional mics can be strategically positioned to capture both the direct sound of an instrument or vocalist, along with the room’s natural ambience.
• Achieving a specific sonic aesthetic: The proximity effect and the figure-8 pattern contribute to a unique sound that can be desirable for certain musical styles or voice-over applications.
• Creating natural, phase-coherent stereo images: The figure-8 pattern is essential for mid-side (M-S) stereo recording.

What You Will Learn

This guide will provide you with a comprehensive understanding of bi-directional microphones, equipping you with the knowledge and skills to use them effectively in a variety of recording scenarios. We will explore the following topics:

• A deep dive into the figure-8 polar pattern and its implications.
• An introduction to ribbon microphones, the most common type of bi-directional mic.
• Techniques for taming and utilizing the proximity effect.
• Creative stereo recording techniques using bi-directional microphones.
• Practical applications for bi-directional microphones in diverse recording environments.

By the end of this guide, you will be able to confidently select, position, and utilize bi-directional microphones to achieve professional-quality recordings.

Bi-directional microphones, often overlooked in favor of their cardioid and omnidirectional cousins, possess a unique sonic signature and set of characteristics that make them invaluable tools for specific recording applications. They capture sound from the front and back of the microphone capsule while rejecting sound from the sides, a pattern visualized as a figure-8. This distinct polar pattern opens up creative possibilities for capturing nuanced performances, achieving natural stereo recordings, and even isolating sound sources in challenging acoustic environments.

Understanding the Figure-8 Polar Pattern: Front and Back

The allure of the bi-directional microphone lies squarely within its distinctive figure-8 polar pattern. It’s more than just a diagram; it’s a roadmap to controlled sound capture and creative recording possibilities. Let’s delve into the intricacies of this pattern and explore its practical applications.

Decoding the Figure-8: A Zone of Sensitivity

Unlike omnidirectional microphones, which capture sound from all directions equally, or cardioid microphones, which primarily focus on sound from the front, the figure-8 pattern carves out a specific zone of sensitivity.

Imagine an invisible "8" surrounding the microphone capsule. The microphone is most sensitive to sound arriving from directly in front (0 degrees) and directly behind (180 degrees).

Sounds originating from these angles are captured with the highest gain.

Visualizing the Pattern

To truly grasp the figure-8, it’s essential to visualize it. Picture a microphone placed at the center of a circle.

Two overlapping circles, one in front and one behind the mic, represent the areas of maximum sensitivity. This visual representation clarifies how the microphone perceives sound from different directions.

The Power of Side Rejection

One of the most significant advantages of the figure-8 pattern is its exceptional side rejection. Sound arriving from the sides of the microphone (90 degrees off-axis) is significantly attenuated, often by as much as 20-30dB.

This side rejection is crucial for minimizing unwanted noise and spill from instruments or sound sources positioned to the sides of the microphone. It effectively isolates the desired sound sources, creating a cleaner and more focused recording.

Imagine recording a duet with two singers facing each other, each positioned in front of one side of the microphone. The figure-8 pattern would isolate their voices while minimizing bleed from other instruments in the room.

Practical Applications in Recording

The figure-8 polar pattern finds its utility in a wide range of recording contexts.

• Duet Vocals: As mentioned, perfect for capturing two vocalists facing each other, creating a natural blend while minimizing bleed.
• Mid-Side (M-S) Stereo Recording: A classic stereo technique where a cardioid or omnidirectional microphone captures the "mid" signal, and a bi-directional microphone captures the "side" information. This technique offers excellent mono compatibility and adjustable stereo width.
• Room Ambience: Positioned strategically, a bi-directional microphone can capture the natural ambience of a room, adding depth and space to a recording.
• Isolating Instruments: In a live recording scenario, a figure-8 microphone can be used to isolate a specific instrument while rejecting sound from other instruments on stage.

Considerations for Optimal Use

While the figure-8 pattern offers unique advantages, it’s important to consider the acoustic environment.

Since the microphone captures sound from both the front and back, the rear side should be positioned to capture desirable reflections or, conversely, away from unwanted noise sources.

Careful microphone placement and acoustic treatment are key to maximizing the benefits of the figure-8 polar pattern.

Decoding the intricacies of the figure-8 polar pattern reveals its power in controlling sound capture, but it’s essential to explore the hardware that often embodies this pattern: the ribbon microphone. For decades, ribbon microphones have been synonymous with the figure-8, each complementing the strengths of the other. Let’s examine why.

Ribbon Microphones: The King of the Figure-8

Ribbon microphones occupy a unique position in the world of audio recording. Often hailed for their vintage warmth and natural sound, they are inextricably linked with the figure-8 polar pattern. But what makes this pairing so common, and what sonic characteristics define these microphones?

The Ribbon Element: A Natural Bi-Directional Transducer

At the heart of a ribbon microphone lies its namesake: a thin, corrugated strip of metal, typically aluminum, suspended within a magnetic field. When sound waves strike this ribbon, it vibrates. These vibrations induce an electrical current proportional to the sound’s amplitude and frequency.

The figure-8 pattern arises naturally from this design. The ribbon is equally exposed to sound from the front and back. This inherent symmetry dictates that the microphone will be equally sensitive to sounds arriving from those two directions.

Critically, sound waves arriving from the sides exert equal pressure on both sides of the ribbon simultaneously, resulting in cancellation and effective side rejection. This inherent side rejection is a crucial attribute of the figure-8 pattern.

The Symbiotic Relationship: Why Ribbons Favor Figure-8

While other microphone designs can implement a figure-8 pattern, the ribbon microphone achieves it with an elegant simplicity. There is no complex electronic circuitry needed to artificially create the polar pattern. It is a direct consequence of the ribbon element’s physical properties.

This natural implementation translates to a more consistent and accurate figure-8 pattern compared to designs that electronically mimic it. The result is superior side rejection and a more focused capture from the front and rear lobes.

The marriage of ribbon technology and the figure-8 pattern gives rise to numerous creative recording options in controlled recording environments.

Sonic Signatures: Warmth, Smoothness, and Sensitivity

Ribbon microphones are celebrated for their distinct sonic characteristics:

• Warmth: They tend to exhibit a smooth, rolled-off high-frequency response, which gives recordings a pleasing warmth and avoids harshness.
• Smoothness: The ribbon element reacts quickly to transients, yielding smooth and natural recordings, especially with vocals and instruments.
• Sensitivity: They are known for their sensitivity, but it’s a double-edged sword, requiring quiet preamps and careful handling.

These characteristics make ribbon microphones exceptionally well-suited for capturing sources that can sound brittle or harsh with other microphones. They excel at taming sibilance in vocals and smoothing out the aggressive transients of brass instruments.

However, it’s important to note that their sensitivity can make them more susceptible to noise and require higher gain preamps.

The ribbon microphone’s sonic signature, combined with the controlled capture of the figure-8 pattern, makes it a formidable tool for achieving refined and nuanced recordings.

That natural, airy quality that ribbon microphones bring to a recording can sometimes come with a trade-off. While the figure-8 pattern excels at capturing nuanced audio and rejecting unwanted noise, its inherent design often amplifies a phenomenon known as the proximity effect, influencing low-frequency response. Mastering this effect is key to unlocking the full potential of bi-directional microphones.

Taming the Proximity Effect: A Bi-Directional Microphone’s Double-Edged Sword

The proximity effect is a change in frequency response dependent on the distance between a microphone and the sound source. It manifests as an increase in low-frequency response as the microphone gets closer to the source.

Understanding the Proximity Effect

In simpler terms, the closer you get to a bi-directional microphone, the bassier the recording becomes.

This isn’t necessarily a bad thing, but it must be understood and controlled. Failing to do so can result in muddy, boomy recordings that lack clarity.

The proximity effect arises from the way pressure gradient microphones, including ribbons and some condensers in figure-8 mode, respond to sound. They measure the difference in pressure between the front and back of the diaphragm.

As the sound source gets closer, this pressure difference becomes more pronounced, particularly for low frequencies, leading to the bass boost.

The Impact on Bi-Directional Microphones

Bi-directional microphones are particularly susceptible to the proximity effect due to their inherent design. The equal sensitivity to sound from the front and rear diaphragms exacerbates the pressure differential, amplifying the low-frequency boost.

This can be particularly noticeable when recording vocals or instruments with strong low-frequency content, such as bass guitars or kick drums.

A singer who moves even slightly closer to the microphone can dramatically alter the tonal balance of the recording.

Techniques for Taming the Beast

Fortunately, the proximity effect isn’t something to be feared. Instead, it can be managed and even exploited for creative purposes. Here are several techniques to tame (or weaponize) the proximity effect:

• Distance Control: This is the most straightforward method. Simply maintain a consistent distance from the microphone. Experiment to find the "sweet spot" where the bass response is balanced and doesn’t overwhelm the other frequencies. Even small changes in distance can have a dramatic effect.

• Microphone Placement: Subtle adjustments to the microphone’s position can significantly impact the proximity effect. Try angling the microphone slightly away from the sound source, or moving it slightly to the side. This can help reduce the bass build-up without sacrificing the overall sound quality.

• High-Pass Filter (HPF): A high-pass filter, also known as a low-cut filter, attenuates frequencies below a certain point. Engaging an HPF on your microphone preamp or audio interface can effectively reduce the low-frequency boost caused by the proximity effect. Experiment with different HPF settings to find the optimal balance for your recording.

• Pop Filter: While primarily designed to reduce plosives (bursts of air from "p" and "b" sounds), a pop filter also adds a small amount of distance between the sound source and the microphone, mitigating the proximity effect to a degree.

• Equalization (EQ): EQ can be used to surgically remove unwanted low-frequency buildup after the recording. However, it’s generally preferable to minimize the proximity effect during the recording process using the other techniques mentioned above.

Harnessing the Proximity Effect Creatively

The proximity effect isn’t always a problem to be solved. Skilled sound engineers and musicians often use it creatively to enhance their recordings:

• Adding Warmth: For vocals that sound thin or brittle, a controlled amount of proximity effect can add warmth and body. This is a classic technique used in radio broadcasting to give voices a richer, more authoritative sound.

• Emphasizing Low Frequencies: On instruments like acoustic guitar or upright bass, strategic use of the proximity effect can bring out the low-end frequencies and create a fuller, more resonant sound.

• Dynamic Performance: Vocalists can use subtle movements towards and away from the microphone to create dynamic variations in their performance. This technique adds expressiveness and nuance to the recording.

Achieving a Balanced Sound

Ultimately, the key to taming the proximity effect is understanding its behavior and learning how to control it.

Experiment with different techniques, listen critically, and find what works best for your specific recording situation.

By mastering this double-edged sword, you can unlock the full potential of bi-directional microphones and achieve truly exceptional recordings.

That sensitivity, when managed well, offers a world of sonic possibilities, and it leads us to one of the most compelling applications of bi-directional microphones: stereo recording. Capturing a wide, immersive soundscape becomes remarkably achievable with the inherent capabilities of these microphones.

Creative Stereo Recording Techniques with Bi-Directional Mics

Bi-directional microphones aren’t just for isolating individual sounds; they can be powerful tools for creating expansive stereo images. The figure-8 polar pattern, with its distinct front and rear lobes, allows for unique spatial capture techniques that other microphone types simply can’t replicate. Let’s explore the exciting world of stereo recording with bi-directional microphones.

Unlocking Stereo Potential with Figure-8

Stereo recording aims to recreate the spatial impression of a sound source, providing listeners with a sense of width, depth, and directionality.

Bi-directional microphones excel in this area because their polar pattern inherently captures sound from multiple directions. This allows for specialized configurations.

The most popular of these configurations, and a technique that truly shines with bi-directional microphones, is Mid-Side (M-S) recording.

Deep Dive into Mid-Side (M-S) Recording

M-S recording is a powerful stereo technique that offers exceptional mono compatibility and flexible width control. It uses two microphones:

• A "Mid" microphone: This captures the center of the sound source. It’s often a cardioid microphone, but other polar patterns can be used.

• A "Side" microphone: This is a bi-directional microphone placed with its null points (sides) facing the sound source. It captures the ambience and spatial information from the sides.

The magic of M-S recording lies in how these signals are processed.

The Side microphone’s signal is duplicated, and one copy is polarity-inverted.

These signals are then summed with the Mid microphone’s signal to create the left and right channels of the stereo image.

Setting Up Your M-S Rig

Here’s a step-by-step guide to setting up an M-S recording rig:

1. Choose Your Microphones: Select a cardioid (or other suitable pattern) for the Mid and a bi-directional microphone for the Side. Ribbon microphones are often favored as Side microphones due to their natural sound.

2. Position the Microphones: Place the Mid microphone facing the sound source. Position the bi-directional (Side) microphone with its side (null point) facing the sound source, perpendicular to the Mid microphone. The capsules should be as close as possible to minimize phase issues.

3. Record the Signals: Record the Mid and Side microphone signals on separate tracks in your DAW (Digital Audio Workstation).

4. Create the Stereo Image:

   • Duplicate the Side track.
   • Invert the polarity of one of the Side tracks.
   • Pan one Side track hard left and the other hard right.
   • Sum the Mid track with the panned Side tracks to create the left and right channels.

Fine-Tuning the M-S Image

The real beauty of M-S recording is the ability to adjust the stereo width after recording. By changing the relative levels of the Mid and Side signals, you can control the wideness of the stereo image.

• Increasing the Side signal widens the image, making the sound more spacious.
• Decreasing the Side signal narrows the image, increasing the focus and mono compatibility.

Beyond M-S: Other Stereo Techniques

While M-S is a standout technique, bi-directional microphones can also be used in other stereo configurations, although often in conjunction with other microphone types:

• Blumlein Pair: This technique uses two bi-directional microphones angled at 90 degrees to each other. It provides a wide stereo image and excellent ambience capture. However, it can be more prone to phase issues than M-S.

• Spaced Pair (with Figure-8): While traditionally using omnidirectional or cardioid mics, incorporating a bi-directional mic in a spaced pair can add interesting ambience from the rear, creating a unique stereo perspective.

M-S vs. Other Stereo Techniques

Feature	M-S Recording	Blumlein Pair	Spaced Pair (with Figure-8)
Microphone Types	Cardioid (Mid) + Bi-directional (Side)	Two Bi-directional Microphones	Various, including Bi-directional
Stereo Width	Adjustable post-recording	Fixed by microphone angle	Dependent on microphone spacing
Mono Compatibility	Excellent	Good, but can be prone to phase cancellation	Can be problematic, especially at wider spacings
Ambience Capture	Good, controlled by Side signal level	Excellent	Varies based on microphone placement
Complexity	Requires post-processing (duplication and polarity inversion)	Simple setup	Simple setup

Ultimately, the best stereo technique depends on the specific sound source, recording environment, and desired sonic characteristics. However, the versatility and control offered by M-S recording make it a compelling choice for many applications, especially when using bi-directional microphones.

Beyond the Studio: Practical Applications for Bi-Directional Microphones

Bi-directional microphones, often perceived as specialized studio tools, possess a remarkable versatility that extends far beyond controlled recording environments. Their unique figure-8 polar pattern, with its distinct front and rear lobes, opens up a world of creative possibilities in diverse scenarios. Let’s explore some practical applications, showcasing the adaptability and unique character of these microphones.

Stereo Recording Techniques Revisited

As we touched upon earlier, bi-directional microphones are indispensable for certain stereo recording techniques, most notably Mid-Side (M-S) recording.

However, it’s worth reiterating their importance in this context.

The bi-directional microphone in an M-S setup captures the ambience and spatial information, providing a sense of width that is crucial for an immersive stereo image.

Beyond M-S, a Blumlein Pair, which utilizes two figure-8 microphones angled at 90 degrees to each other, can deliver a precise and detailed stereo image with excellent localization.

Vocal Recording: Intimacy and Ambiance

While condenser microphones are often the go-to choice for vocals, bi-directional microphones can offer a unique and compelling alternative, particularly when aiming for a specific aesthetic.

The figure-8 pattern picks up not only the vocalist’s direct sound but also a controlled amount of room ambiance.

This can add a natural depth and warmth to the recording, especially in well-treated acoustic spaces.

However, careful attention must be paid to the room’s acoustics, as unwanted reflections can negatively impact the recording.

Close proximity to the microphone can also accentuate the proximity effect, resulting in a bass-heavy sound that may require careful EQ adjustment.

Capturing Acoustic Instruments

Bi-directional microphones excel at recording acoustic instruments, particularly those with rich harmonic content.

Guitars, strings, and horns can all benefit from the smooth, natural sound reproduction that ribbon microphones (a common type of bi-directional mic) are known for.

Placing a bi-directional microphone a few feet away from an acoustic guitar, for instance, can capture a balanced blend of the instrument’s body and the surrounding air, resulting in a warm and organic tone.

The microphone’s side rejection can also be used to minimize unwanted sounds from other instruments or the surrounding environment.

Interviews and Dialogue

The bi-directional polar pattern is ideally suited for recording interviews or dialogues between two people.

By positioning the microphone between the speakers, each person can be captured with equal clarity and presence.

This eliminates the need for multiple microphones and simplifies the recording setup.

Furthermore, the side rejection of the figure-8 pattern helps to minimize unwanted background noise. This ensures that the focus remains on the conversation.

However, it is important to maintain a consistent distance from the microphone.

This ensures that both speakers are recorded at a similar level and that the proximity effect is consistent across both voices.

Podcasting and Voice-Over Work

While not the most common choice, bi-directional microphones can be creatively utilized in podcasting and voice-over work, particularly when aiming for a specific aesthetic.

For solo podcasting, a bi-directional microphone can capture a more natural and less isolated sound compared to a cardioid microphone.

By positioning the microphone slightly off-axis, the proximity effect can be used to add warmth and depth to the voice.

In voice-over work, bi-directional microphones can be used to create a sense of intimacy and presence, particularly for narration or character voices.

However, careful attention must be paid to the room’s acoustics to avoid unwanted reflections or echoes.

In conclusion, while bi-directional microphones might seem specialized, their applications are surprisingly diverse. Understanding their unique characteristics and leveraging their figure-8 polar pattern can unlock a world of creative possibilities in various recording scenarios, both in and out of the traditional studio environment.

Hope this helped you find the right bi directional microphones for your needs! Happy recording, and don’t hesitate to experiment to find what works best for your situation.