Sega Genesis Soundfonts Online

The 16-Bit Gritty Magic: A Guide to Sega Genesis Soundfonts If you close your eyes and hear the metallic "twang" of a bassline or the crunchy explosion of a snare drum, there’s a good chance your brain is teleporting back to the early 90s. The Sega Genesis

(or Mega Drive) had a sound unlike any other console of its era. While the SNES aimed for orchestral realism, the Genesis went for raw, synthesized energy. Today, thanks to soundfonts

, you don't need a vintage console and a soldering iron to capture that vibe. Whether you’re a synthwave producer or a game dev, here is everything you need to know about Sega Genesis soundfonts. Why Does the Genesis Sound So "Crunchy"? The secret sauce of the Genesis was the Yamaha YM2612 sound chip. Unlike modern samplers, this chip used FM Synthesis

(Frequency Modulation). Instead of playing back recorded sounds, it used mathematical operators to "carve" sounds out of thin air. This resulted in: Metallic Textures: Perfect for industrial and sci-fi scores. The Iconic "Slap" Bass: Sonic the Hedgehog Streets of Rage Distinct Distortion: A gritty, lo-fi charm that cuts through any mix. Top Soundfonts to Get You Started

A soundfont (.sf2) is essentially a digital container of these 16-bit instrument presets. Here are the most popular ones used by the community today: The "General User" GS Genesis Font:

A great all-rounder that maps classic Genesis-style FM patches to standard MIDI instruments. Sonic the Hedgehog 1, 2, & 3 Rip:

These are direct extractions from the game code. If you want that exact "Green Hill Zone" pluck, this is where you find it. Streets of Rage 2 Collection:

Created by the legendary Yuzo Koshiro, these sounds are the gold standard for 16-bit electronic dance and house music. VRC6/OPLL Hybrid Fonts:

For those who want to mix the Genesis grit with a bit of 8-bit NES flair. How to Use Them in Your Music

You don't need expensive software to start "blasting processing" your tracks. Get a Player: Download a free Soundfont player VST like Load the .sf2:

Drop your Genesis soundfont into the player within your DAW (FL Studio, Ableton, Logic, etc.). Embrace the Limitations: To stay authentic, try to limit yourself to 6 channels

of audio. The original hardware couldn't handle more than that! Bit-Crush It:

To get that extra "hardware" feel, add a slight bit-crusher or a low-pass filter to mimic the console's internal circuitry. Where to Find Them?

The best places to hunt for these digital relics are community-driven sites like Musical Artifacts Slippy's Dream World

. Most are free to download and maintained by passionate retro-gaming fans. If you want to go beyond soundfonts and actually the sounds, check out Plogue Chipsynth MD

. It’s a bit-accurate emulation of the hardware that lets you tweak the FM operators yourself. DAW plugins

best emulate the Genesis FM synthesis beyond basic soundfonts?

The Sega Genesis Go to product viewer dialog for this item. (or Mega Drive) is renowned for its distinctive gritty, metallic, and punchy audio, primarily driven by the Yamaha YM2612 FM synthesis chip. While the original hardware generates sound through frequency modulation synthesis, soundfonts ( SF2cap S cap F 2

) allow modern composers to use sampled versions of these iconic instruments within Digital Audio Workstations (DAWs). Popular Sega Genesis Soundfonts

Finding a high-quality soundfont often involves looking for collections that capture the console's "General MIDI" equivalents or specific game patches:

The Ultimate Megadrive Soundfont: A widely used collection available on Polyphone that maps classic Genesis instruments to the General MIDI standard.

The Absolute Sega FM Soundfont V2: A massive 264 MB compilation found on Musical Artifacts

featuring drum samples, GEMS samples, and instruments sourced from trackers like Deflemask. Sonic 123 SF2

: Often recommended for creators looking to specifically replicate the vibes of the early Sonic the Hedgehog trilogy.

Game-Specific Soundfonts: You can find specialized soundfonts for titles like Toy Story or Olympic Summer Games on community sites like Musical Artifacts. Technical Implementation To use these sounds in your music production: Download: Obtain the

file from reputable community repositories like Musical Artifacts or Polyphone.

DAW Integration: Use a soundfont player plugin. Popular options include the native SoundFont Player in FL Studio or third-party tools like Plogue Sforzando.

Limitations: Because soundfonts are sampled (recordings of sounds), they can be more limiting than "true" FM synthesis. For more authentic control, experts often suggest VSTs like Genny or Plogue Chipsynth MD, which emulate the chip's synthesis in real-time. Comparison: Genesis vs. SNES

Title: The Ghost in the Chip: How a Pizza-Eating Engineer Created the Sound of a Generation

Part 1: The Problem (1990)

Marco was a bedroom producer in 2020, but his heart lived in 1992. He loved the gritty, snarling basslines of Streets of Rage 2 and the punchy, metallic drums of Sonic the Hedgehog. He wanted that sound in his modern music software.

He opened his DAW, searched for “Sega Genesis soundfont,” and downloaded a file. When he loaded it, he was hit with a wave of thin, screechy noise. “This sounds like a broken ringtone,” he groaned. “Why can’t I make it sound like the real thing?”

To understand, Marco had to travel back in time to meet a fictional engineer named Kenji.

Part 2: The Hardware Truth (1991)

Kenji worked for Sega in Tokyo. His boss gave him a near-impossible task: “Make a sound chip that can do arcade-quality music and sound effects, but keep it cheap enough to fit in a home console.”

Kenji’s solution was the Yamaha YM2612 (and a separate Texas Instruments PSG chip for retro compatibility). Unlike the Super Nintendo, which used sampled instruments (actual recordings of pianos and violins squeezed into memory), Kenji’s chip was an FM synthesizer.

FM Synthesis works by using sine waves to modulate other sine waves, creating bright, glassy, metallic tones.
The Cost: No real samples. No piano recordings. Everything was math.
The Limitation: Only 6 simultaneous channels of sound. And no built-in reverb or chorus.

Marco’s “broken ringtone” soundfont failed because someone had simply recorded raw YM2612 output without the context—without the mixing desk, without the analog amplifier, and without the specific tricks composers used.

Part 3: The Three Secrets of the Genesis Sound

Marco found an old forum post by a retired game composer. It revealed three secrets:

Secret #1: The “Ear Bleed” Filter The Genesis had a harsh, high-frequency “glare” when played directly. Real composers didn’t fight it—they masked it. They layered a soft, noisy “ghost” channel (using the PSG chip) underneath the main bass to warm it up. A good soundfont needs to emulate this warmth, not just the raw sine waves.

Secret #2: The Missing Velocity On a piano, you hit a key softly or hard. The Genesis had no “velocity sensitivity.” Every note was full volume. To get dynamics, composers had to manually draw volume automation (called “key scaling”). A useful soundfont must include pre-programmed volume curves that mimic this.

Secret #3: The DAC Quirk The Genesis’s digital-to-analog converter (DAC) wasn’t perfect. It added a subtle, crunchy distortion when multiple loud notes played at once. That crunch is what makes the bass in Comix Zone punch so hard. Modern soundfonts that sound “too clean” miss this entirely.

Part 4: The Build

Armed with this knowledge, Marco stopped downloading random soundfonts and built his own toolkit:

He sourced the right raw material: He found a “YM2612 Direct Capture” pack—recordings taken directly from the chip’s output pins, before the analog stage.
He added an analog console emulator: He ran the sounds through a free plugin called “TAL-DAC” (emulates old samplers) and another called “ChowTape Model” (emulates cassette warmth). He set both to “low fidelity, high character.”
He built a drum kit from scratch: He sampled the kick from Golden Axe, the snare from Shinobi III, and the hi-hat from Thunder Force IV. He layered them with a tiny bit of white noise to mimic the PSG “ghost channel.”
He created a “bass ducker”: He set up a sidechain compressor so that when the kick drum hit, the bass guitar briefly dropped in volume by 3dB. This mimicked how the limited 6 channels would “fight” for headroom.

Part 5: The Result

Marco loaded his custom soundfont into a modern track. He played a simple bassline. It snarled. He added a lead. It sang with that glassy, slightly unstable pitch that only FM can make.

He compared it to his old “broken ringtone” soundfont. The difference was night and day.

Old soundfont: Thin, screechy, lifeless.
New soundfont: Fat, punchy, breathing—it sounded like a Genesis record, not a Genesis schematic.

He uploaded a beat made entirely with his soundfont. The comments exploded: “How did you get that authentic SEGA bass?” “This sounds like it’s running on real hardware!”

Useful Takeaways (The Moral)

If you want a useful Sega Genesis soundfont today, do not just download the first .sf2 file you find. Instead:

Look for “processed” or “analog-captured” soundfonts, not raw YM2612 dumps. The raw chip sounds harsh.
Layer in a touch of noise or saturation to mimic the console’s imperfect output stage.
Manually automate your note velocities – the Genesis ignores them, but your DAW doesn’t. Use velocity to shape filter cutoffs instead of volume.
Limit yourself to 6 notes at once to force creative voice stealing, just like old composers.
Check out modern tools like VOPM (free FM synth), Genny (tracker), or Super Audio Cart (Kontakt library) which do the heavy lifting for you.

The ghost of Kenji’s little chip isn’t dead. It’s just waiting for someone who understands that limitations, embraced correctly, become a signature sound.

In the late 1980s, the "bits wars" were about more than just graphics; they were about the grit and crunch of FM synthesis. While the competition focused on orchestral samples, the Sega Genesis Go to product viewer dialog for this item. leaned into the metallic, industrial heart of the Yamaha YM2612 sound chip.

This is the story of how that "16-bit" sound evolved from a console limitation into a beloved modern soundfont. The Legend of the Metallic Growl

In 1989, the Sega Genesis arrived with a distinct audio personality. Unlike the Super Nintendo's cleaner, sample-based sounds, the Genesis used frequency modulation (FM) to literally build its instruments from scratch using mathematical operators. This gave games like Streets of Rage and Sonic the Hedgehog their signature "slap bass" and aggressive synth leads. From Hardware to Soundfonts

As the era of physical cartridges faded, producers and hobbyists didn't want to lose that specific crunch. They began "ripping" the instrument presets directly from game ROMs. By capturing the unique timbre of the Yamaha YM2612

, they created Soundfonts (.sf2 files)—digital libraries that allow modern musicians to play those exact 1990s sounds on modern computers.

Today, these soundfonts are staples in modern music production:

The Lo-Fi Movement: Artists use Genesis soundfonts to inject "nostalgic grit" into hip-hop and synthwave tracks.

Indie Game Devs: Developers of "retro-style" games use them to achieve authentic 16-bit aesthetics without needing the original 1988 hardware. sega genesis soundfonts

Digital Workstations: You can now load a "Mega Drive" soundfont into FL Studio or Soundtrap, turning a $2,000 laptop into a $189 console from 1989. Why It Still Matters

The Sonic Boom of Soundfonts: Uncovering the Magic of Sega Genesis Music

The Sega Genesis, released in the late 1980s, was a powerhouse of gaming innovation, introducing us to iconic characters like Sonic the Hedgehog and Streets of Rage. But beneath its sleek design and addictive gameplay, the Genesis concealed another secret weapon: its incredible sound capabilities. In this blog post, we'll dive into the fascinating world of Sega Genesis soundfonts, the unsung heroes behind the console's unforgettable music.

What are soundfonts?

For those unfamiliar, soundfonts are collections of audio samples used to generate music and sound effects in electronic devices. Think of them as digital instruments, comprising a range of tones, textures, and timbres that bring games to life. The Sega Genesis soundfont, in particular, was a custom-designed set of samples created by Yamaha, the console's audio hardware provider.

The Sega Genesis soundfont: a masterpiece of audio engineering

The Sega Genesis soundfont consists of 61 unique audio samples, which were cleverly manipulated by game developers to create a staggering variety of sounds. These samples were stored in the console's Yamaha YM2612 sound chip, which used a combination of digital signal processing and analog synthesis to produce the final audio output.

The soundfont included a range of instruments, from standard PCM (pulse-code modulation) samples like percussion, bass, and piano, to more exotic textures like string and vocal samples. The samples were cleverly arranged to allow for a wide range of tonal variations, enabling developers to craft distinctive soundtracks that perfectly complemented the games.

Legendary soundtracks, powered by soundfonts

The Sega Genesis soundfont was instrumental (pun intended) in creating some of the most iconic game soundtracks of all time. Who can forget the mesmerizing loop of Sonic the Hedgehog's Green Hill Zone, or the brooding ambiance of Phantasy Star II's soundtrack? These tunes were made possible by the creative use of the Genesis soundfont.

Some notable examples of games that showcased the Sega Genesis soundfont include:

Sonic the Hedgehog (1991): The Green Hill Zone theme, with its bright, bouncy melody, perfectly encapsulated the game's sense of speed and energy.
Streets of Rage (1991): The game's pulse-pounding soundtrack, with its driving drum machine beats and synthesized basslines, was a perfect fit for the side-scrolling beat-em-up.
Phantasy Star II (1989): The sci-fi RPG's soundtrack, featuring lush strings and eerie ambiance, demonstrated the soundfont's versatility in creating complex, atmospheric soundscapes.

The art of soundfont manipulation

To get the most out of the Sega Genesis soundfont, developers employed a range of creative techniques. They would often:

Re-pitch and re-sample: By adjusting the sample rate and pitch, developers could create a wide range of tones and textures from a single sample.
Layering and stacking: By combining multiple samples, developers could craft rich, layered soundscapes that added depth to the game's audio.
Envelope shaping: By manipulating the sample's attack, decay, sustain, and release (ADSR) envelope, developers could control the dynamics and expression of the sound.

Legacy and influence

The Sega Genesis soundfont has had a lasting impact on the world of video game music. Its innovative use of audio samples and synthesis techniques paved the way for future console sound design. The soundfont's limitations, ironically, became a driving force behind the creative solutions developers employed to produce memorable music.

The Sega Genesis soundfont has also inspired a new generation of chiptune musicians, who continue to push the boundaries of what can be achieved with retro hardware. The demoscene, a community of artists and programmers, has also been influenced by the Genesis soundfont, with many creations showcasing the console's audio capabilities.

Conclusion

The Sega Genesis soundfont was a crucial component in the creation of some of the most iconic game soundtracks of all time. Its clever design and manipulation by game developers resulted in a treasure trove of audio gems that continue to captivate gamers and music enthusiasts alike. As we look back on the Sega Genesis era, it's clear that the soundfont played a vital role in shaping the sonic identity of the console, and its influence can still be felt today.

Sega Genesis soundfonts are digital collections of audio samples captured from the console's iconic hardware—specifically the Yamaha YM2612 (FM synthesis) and Texas Instruments SN76489 (PSG) chips. These files (typically in

format) allow modern producers to recreate the gritty, metallic FM bass and 8-bit percussion characteristic of 16-bit era titles like Sonic the Hedgehog Streets of Rage Popular Sega Genesis Soundfont Libraries How to make Sega Genesis Music (in a DAW)

Sega Genesis soundfonts (typically in .sf2 format) are collections of audio samples and parameters designed to recreate the distinct FM-synthesis-driven audio of the 16-bit console. Because the original Sega Genesis used the Yamaha YM2612 chip to generate sound in real-time rather than playing back samples, soundfonts are often "sampled" versions of these synthesized sounds or specific drums and FX used in iconic games. Essential Components

FM Synthesis Simulation: Most soundfonts focus on the "gritty" and "metallic" textures of the YM2612. These include the famous "Sega Slap Bass," distorted electric guitars, and crystalline pads.

PCM Drums: The Sega Genesis had a dedicated channel for low-bitrate (8-bit) samples, mostly used for percussion. Soundfonts frequently bundle these "crunchy" drum hits.

The GEMS Collection: Many available soundfonts are based on the General Instrument (GEMS) driver used by western developers, which has a distinct, recognizable sound compared to Japanese-developed titles. Popular Soundfonts & Resources

Jnsgm2.sf2: Highly regarded by the MIDI community for being exceptionally well-balanced and space-efficient (roughly 32 MB). Project 2612

: While primarily a music archive site, it is a frequent jumping-off point for finding sound banks and instrument rips from specific games. GeneralUser GS

: While a general-purpose soundfont, it is often used in conjunction with Genesis banks for a hybrid retro-modern sound. How to Use Them

To use these sounds in modern music production, you generally need two things: The Soundfont File (.sf2): The actual library of sounds.

A Soundfont Player (VST/AU): Software like Sforzando, FluidSynth, or built-in samplers in DAWs like FL Studio to load and play the file. Legal and Creative Context The 16-Bit Gritty Magic: A Guide to Sega

Most Sega Genesis soundfonts are fan-made projects that sample original hardware or game data. From a copyright perspective, these are often considered "grey area" tools. They are widely used in genres like Synthwave, Chiptune, and even experimental metal projects like Gonemage, which blends black metal with Sega-inspired textures.

The Sega Genesis is often remembered as the "grittier" alternative to its contemporaries, a reputation largely forged by its distinctive FM synthesis sound. Unlike the sample-based audio of the Super Nintendo, the Genesis utilized the Yamaha YM2612 chip, which generated sound through frequency modulation. In the modern era of digital music production, the quest to replicate this crunchy, metallic, and high-energy aesthetic has led to the creation and widespread use of Sega Genesis soundfonts. These digital toolsets allow composers to bridge the gap between 16-bit nostalgia and modern fidelity, preserving a unique chapter of audio history while enabling new creative expressions.

The core of the Genesis sound lies in its architectural limitations. The YM2612 chip featured six FM voices, often supplemented by a programmable sound generator (PSG) and a single channel for low-quality PCM samples—most famously used for the "SEGA!" chant or digitized drums. This setup produced a signature "metallic" timbre that was notoriously difficult to master but yielded iconic results in titles like Sonic the Hedgehog and Streets of Rage. Because the hardware didn't rely on recorded instrument loops, the "instruments" were actually complex mathematical algorithms. Modern soundfonts attempt to capture these specific algorithms and sample the resulting waveforms, giving producers a "plug-and-play" version of those historic textures without needing to program a vintage synthesizer from scratch.

For contemporary musicians, Sega Genesis soundfonts offer more than just a trip down memory lane; they provide a specific "lo-fi" texture that is currently in high demand. The aliasing noise and the specific distortion produced by the Genesis’s hardware—often referred to as the "ladder effect"—give the audio a punchy, aggressive quality that cuts through a mix. By using soundfonts sampled directly from the hardware, producers can inject their tracks with a sense of "bit-crushed" authenticity. These soundfonts have become staples in genres like synthwave, chiptune, and even modern trap music, where the sharp, FM-synthesized basslines of the 90s provide a fresh alternative to standard analog sine waves.

Furthermore, the availability of these soundfonts serves a vital role in digital preservation. As original hardware becomes rarer and more expensive, the digital "sampling" of these sounds ensures that the unique sonic fingerprint of the 1990s isn't lost. Community-driven projects have meticulously archived the soundbanks of hundreds of Genesis games, allowing anyone with a Digital Audio Workstation (DAW) to experiment with the same tools used by legendary composers like Yuzo Koshiro or Masato Nakamura. This democratization of vintage sound means that the legacy of the Genesis continues to evolve, as a new generation of artists repurposes these 16-bit textures for entirely new musical contexts.

Ultimately, Sega Genesis soundfonts represent the intersection of technological limitation and creative enduringness. What was once a byproduct of cost-effective hardware in the late 80s has become a prestigious aesthetic choice in the 21st century. These soundfonts do more than just mimic an old console; they capture a specific vibe of digital aggression and industrial warmth that remains unmatched by modern synthesis. As long as artists seek to blend the nostalgic with the novel, the crunchy, distorted, and unmistakable ring of the Sega Genesis will continue to echo through modern speakers.

If you'd like to dive deeper into the technical side or find specific tools, I can help you:

Locate specific VSTs that emulate the YM2612 chip (like Genny or Plogue Chipsynth MD).

Find tutorials on how to program FM synthesis for that "metallic" bass sound.

Discover famous soundbanks from specific games like Streets of Rage or Sonic. Which of these

The Sega Genesis (known as the Mega Drive outside North America) defined a generation with its "gritty" and "metallic" sound, powered by FM synthesis. Unlike its competitor, the SNES, which used sample-based audio, the Genesis relied on the Yamaha YM2612 chip to generate complex timbres through Frequency Modulation (FM).

For modern producers, Sega Genesis soundfonts (.sf2 or .sfz files) are the most accessible way to capture this 16-bit nostalgia within a Digital Audio Workstation (DAW) like FL Studio or Ableton Live. Understanding the Genesis Sound Architecture

To use these soundfonts authentically, it is vital to understand the hardware they emulate:

The Iconic Sound of Sega Genesis: Understanding Soundfonts

The Sega Genesis, released in 1988, was a groundbreaking console that brought 16-bit gaming to the masses. One of the key factors that contributed to its success was its distinctive sound. The Sega Genesis sound chip, known as the Yamaha YM2612, was a six-channel FM (Frequency Modulation) synthesizer that produced a wide range of timbres and textures. To replicate and manipulate these sounds, sound designers and musicians use soundfonts.

What are Soundfonts?

A soundfont is a collection of audio samples or algorithms that mimic the sound of a particular instrument, synthesizer, or sound chip. In the context of Sega Genesis sound design, a soundfont typically consists of a set of FM synthesis parameters, sample data, or a combination of both. These soundfonts allow producers and musicians to recreate the iconic sounds of the Genesis, from the pulsing basslines to the percussive and melodic textures.

Sega Genesis Soundfont Types

There are two primary types of Sega Genesis soundfonts:

FM Soundfonts: These soundfonts directly emulate the Yamaha YM2612 chip's FM synthesis capabilities. They contain the necessary parameters to generate the same sounds that the original chip produced, including the algorithms, operators, and feedback configurations.
Sample-based Soundfonts: These soundfonts use sample data to recreate the sounds of the Genesis. They often involve recording and editing individual samples of the console's sounds, then mapping them to a MIDI keyboard or other control system.

Applications of Sega Genesis Soundfonts

Sega Genesis soundfonts have numerous applications in music production, sound design, and chiptune music:

Music Production: Producers and musicians use Genesis soundfonts to create music that pays homage to the classic console or to add a retro flair to their compositions.
Video Game Soundtracks: Sound designers and composers use Genesis soundfonts to create authentic soundtracks for games that evoke the spirit of 16-bit classics.
Chiptune Music: Chiptune artists often use Genesis soundfonts to create new music that takes advantage of the console's sonic capabilities.

Popular Sega Genesis Soundfonts

Some notable Sega Genesis soundfonts include:

Genpaks: A set of FM soundfonts for the Korg Prophecy and other synthesizers.
Sega Genesis Soundfont: A sample-based soundfont for use in music production software.
FMGen: A software soundfont that emulates the Yamaha YM2612 chip.

Conclusion

Sega Genesis soundfonts have become an essential tool for sound designers, musicians, and producers looking to tap into the sonic nostalgia of the 16-bit era. By understanding and utilizing these soundfonts, creators can craft music and sound effects that evoke the spirit of classic Sega Genesis games. Whether used in music production, video game soundtracks, or chiptune music, Sega Genesis soundfonts continue to inspire new generations of audio enthusiasts.

Step 2: Import the Bank

Load your player. Drag the .sf2 file onto the interface. You will see a list of "Presets" (e.g., "001: Piano," "034: Bass").

1. The VGM Soundfont by Reality Ragan (The Gold Standard)

This is the crown jewel. The VGM.sf2 (Video Game Music soundfont) is a massive, meticulously compiled library of literally hundreds of instruments ripped directly from Sega Genesis ROMs.

Includes: The exact brass from Streets of Rage, the exact strings from Phantasy Star IV, the exact "punchy square" from Sonic 1.
Pros: Authentic. If you want the literal sound of 1992, this is it. It includes the console's noise floor.
Cons: It’s massive (over 200MB). Some instruments overlap weirdly because different games used different patches for "Piano."
Best for: Remixes and covers that need 100% authenticity.

Overview

Sega Genesis (Mega Drive) sound is driven by the Yamaha YM2612 FM chip (six channels, one usually used for rhythm via an external DAC) and the Texas Instruments SN76489 PSG (three square-wave channels + noise). "Soundfonts" for Genesis typically means collections of instrument definitions or sampled patches and FM presets designed to emulate Genesis timbres in modern samplers, trackers, or FM emulators.

5. Common pitfalls & fixes

| Problem | Solution | |---------|----------| | Sounds too clean / hi‑fi | Add bit crusher (12‑bit, 26 kHz) + low‑pass filter. | | Drums are weak | Layer with Linndrum / 707 samples (common Genesis dev trick). | | No vibrato / pitch bending | Use MIDI pitch bend → YM2612 supports ±1 semitone easily. | | PSG noise too harsh | Low‑pass filter at ~5 kHz. | Title: The Ghost in the Chip: How a

The Essential Sega Genesis Soundfont Libraries (2024 Update)

Whether you are making Chiptune, Synthwave, Hip Hop, or Metal, these are the gold standards.