Aang should have been able to have an offensive specialized form of Airbending, to go along with Zuko’s Lighting Bending, Katara’s Bloodbending and Toph’s Metalbending. Aang should have had an episode to establish that he developed the ability to Soundbend. What it could’ve been is this. Use it to increase or soften noises, creating sonic blasts or stealth movements. A snap could cause a sonic boom and so on. Or hell let’s go by the fanon Soundbending article.
Soundbending is a special subset of techniques within Airbending that allows an Airbender to sonokinetically generate sound waves and manipulate already existing ones as they travel through the air.
The key to Soundbending is a combination of flexibility and endurance, finding and following the path of resistance as well as enduring enemies' attacks until the right opportunity to counterattack reveals itself, then striking with unyielding force. Soundbending's strength is its offensive capabilities which, rather than supporting a separate set of defensive methods, are transformed into defenses and opposition - offense into defense. Soundbenders can overwhelm many opponents at once with large and powerful attacks that could prove fatal; however due to the pacifist nature of the Air Nomads such attacks are rarely used. Just like Waterbending and Earthbending, Soundbending has a distinct use of offense and defense. Instead of sacrificing defense for more powerful offensive tactics or allowing defense to become offense, Soundbending transforms offense into defense, utilizing positive and negative jing.
Sound Manipulation: By using circular movements, Soundbenders build up massive inertia; this buildup of energy is released as a massive, overwhelming power. It also allows for counterattacks that blast opponents away, mimicking the explosive power of sound waves. Attacks vary from simple noises to shock-waves. Even a simple movement can create an noise, and Soundbenders increase the power of their moves by using the momentum of their movement to simulate louder and more powerful sounds. This is also demonstrated with their use of staffs or fans to increase or create precision within the sound waves. Since sound can affect almost all physical objects, it can also be used to enforce the momentum of thrown objects or manipulate other objects (though requiring a higher degree of precision).
Sound Walls: A Soundbender can create a wall of sound that is thrust at an enemy. This is used to push attacks aside and more often is converted into a defense, allowing them to turn the movement into an defensive ploy at the same moment.
Sound Barrier: This is a more powerful offensive technique where an entire area around a Soundbender is surrounded by a dome of sound. It is used for offense, a large-scale hemispherical sound wall, and it can be used for defense.
Sound Blast: A offensive move involving a direct pulse or jet of noise from the hands or feet. The force of the attack is generated more from the bender's own power rather than assisted by momentum. This direct blast can reach further with greater accuracy and is used to inflict greater damage.
Sound Punch/Kick: Another offensive move, Sound punches or Sound kicks are small, compressed formations of Sound that can be fired off the fists or feet of a Soundbender. This is similar to the Sound blast yet in the sense that it involves the firing of compressed sound at an enemy in a non-continuous fashion i.e. the bender does not create a single great stream of sound.
Sound Swipe: The Sound Swipe is a dual defensive and offensive technique in which an Soundbender conjures a crescent-moon shaped construct of sound capable of deflecting colossal projectiles; (such as the catapulted flaming rocks often used by the Fire Navy ships) and sending them off-course. In some instances these projectiles can be redirected back at the attacker.
Sonic Scream: Very similar to a standard Sound blast but created from the mouth and lungs. It requires extremely good breath control to employ effectively. Size and focus is more easily controlled, including narrow jets that can strike targets as small as insects, to large shock-waves capable of shattering objects as hard as metal.
Multiple Target Attacks: A Soundbender can send large, wide-spanning waves of sound towards multiple enemies with one long, sweeping motion from an Airbending staff or from the bender's limbs.
Sound Scooter: The Sound Scooter, a form of ground transportation, is a spherical "ball" of sound that can be ridden balancing on it like a top. The Sound Scooter is also shown to be capable of levitating in the air for short periods.
Soundbending Master Level
Sound Vortex: A spinning funnel of sound of various sizes. This can be used to trap and disorient opponents or as a potent defense since it will deflect and repel any objects and can even throw them back at an opponent.
Sound Wake: By running in a circle and instantly building huge momentum, a master Soundbender can shoot a blast of compressed sound shaped like the user's body at a target. This move has great concussive force.
Sound Blades: An offensive move; this involves a focus slicing sound wave that can cut through stone or timber with relative ease. This is frequently conjured with a staff rather than the body, using the narrow profile of the object to create a more focused and precise sound vibrations. This move could prove fatal if used on an individual.
Sound Spout: Similar to the Water Spout, master Soundbenders are able to rotate and control the direction of the Sound Spout enough to levitate them off the ground and remain in the Sound for as long as they wish to or can maintain it.
Sound Concussor: The Sound concussor is a highly destructive move (atypical for Air Nomad principle) in which an Soundbender creates (with use of a staff) a thin wave of Sound that travels quickly along the ground, releasing a near-explosive power when coming into contact with anything in its path. The Sound concussor is even able to run along water before destroying its target.
Mini-shock-waves: This is a smaller scaled version of the Sound vortex which Soundbending masters can use as a means of both combat and transport. By encircling themselves in a spiraling shock-wave, masters can travel at high speeds and even ascend near vertical drops.
Sonar Sense: Skilled Soundbenders are able to sense vibrations through the air, "seeing" by sensing their surroundings and making a mental image of it. It allows for 360 degree "vision", outside of normal line-of-sight. During his training, Aang also developed this ability; he is the only known human to use this technique. Aang used this during a four-way training section with Toph, Katara, and Zuko. Sonar sense can be made so acute that it is capable of sensing even the sounds of ants moving about can identify people by the way they talk. When used in conjecture with Toph's Seismic Sense, the user can effectively see the world around perfectly.
Sound Dampening: Adept Soundbenders can mask any sounds they make which allow them to sneak up on opponents, or make private conversations in a consolidated area. Also they can dampen the sounds of others so an enemy is unable to alert others of the soundbender's presence.
Avatar Level Soundbending
Augmented Soundbending Moves: While in the Avatar State, all of the previously discussed Soundbending moves are generally augmented making them far more powerful in an Avatar than even a bending master.
Shock-waves: In addition to very large and powerful noises, an Avatar level bender can create massive shock-waves at will.
Sound Sphere: Similar to the Air Sphere, this powerful defense surrounds the bender in a sphere of spinning sound that deflects anything coming in at them, levitate across varied distances and can even disintegrate the ground beneath them.
