Preface

Adding sound effects can bolster your sequence in surprising ways, but Online Sequencer probably doesn't have an instrument made for the sound effect you're looking for.  You're going to have to make the sound yourself.

Tip #1: Listen to the sound you're trying to make, in slow motion.

8-bit instruments are some of the best ones for recreating sounds.  Start out by finding an instrument that makes a similar tone to the one you're looking for.  Go watch a YouTube video of the sound you're trying to emulate. Listen to it a bunch of times.  Slow it down to 0.25 speed.  What pitch does it start at, and where does it end?  

One trick I use a lot is to try to whistle the sound.  No really, go ahead.  Like, out loud.  No one will mind.  Whistle it.

I slowed down a Super Mario Bros. video as slow as it would go, and then tried to whistle the same pitch as the "jump" sound effect (for example).  I'd keep whistling the sound while I switched to OS and tried to find the matching note.  Keep switching back and forth between your sequence, and the video, until you get the pitch and speed as close as you can get it.  You may have to alter the BPM of the sequence to get it just right.

Tip #2: Hide the sound behind the music.

Most of the time, your sound effect isn't going to sound exactly like you wanted.  You don't have to make the exact sound you're looking for - you just have to trick people's ears into thinking you did. 

Once you put a sound behind music, it tends to blend in a little more.  Just putting notes over it may not suffice; sometimes you can make a sound more believable by just moving it around a little bit.  Even moving it a quarter note to the left or to the right can make a big difference. 

One example is the ocean sounds in A1A South (starting at measure 22).

I was trying to get a good white noise sound out of Online Sequencer, with little success.  The closest thing to that sound is the 8 bit snare.  Unfortunately, it has a very strong attack; a loud "click", followed by some decent sounding white noise after that.  

Putting lots of 16th notes close to each other didn't work - the click stands out, and if the notes are too close together, it just sounds like a buzzing noise.  So how can you eliminate that click while just leaving white noise?  I put the 8-bit snare at every 8th note, and made sure to have other percussion also at every 8th note.  That way, to your brain, the click sounds like it's part of a hi-hat or other percussion, and the white noise stands out on its own as ocean waves. 

If you just took the "ocean" sounds out of these context, they don't sound anything like ocean sounds. On the right side, there's an example of what it sounds like with, and without, hiding them behind the music.

In addition to hiding the sharp, non-oceany part of the snare, I've provided contextual clues to the listener.  For the segment of the song leading up to measure 22, an actual hi-hat is already present on every 8th note.  Furthermore, the beat is increasingly tropical in nature as the sequence goes on.  So by the time the "ocean" sounds show up, the listener is primed to hear what I wanted them to hear.

Tip #3: Experiment!

Percussion is a great tool for making sound effects.  There are a huge variety of sounds that can be made by OS percussion.  Go through all notes of the drum kit.  If you can't find one that's exactly right, try combining two notes.  Try combining two different drum kits. Try the low-register pizzicato and music box. You never know what you'll encounter that might inspire you.

For Dry Out, the water drips in were completely by accident; I was making a completely different sequence, and happened to hit a percussion note that sounded exactly like the shower dripping in the hotel bathroom.  I ended up building the entire sequence around that one accidental sound effect.

Sometimes you'll stumble across a sound by accident.  You'll be messing around clicking notes on OS, and something just sounds neat.  Or maybe you hear something in the background of someone else's sequence.  Stop what you're doing, and write it down.  Keep a list.  Make a sequence with your favorites, however you like to keep track.  Maybe you don't need that particular sound effect right now, but you might need it someday.  

Your experiments will fail more often than they'll succeed.  Don't get discouraged; keep trying and soon you'll be making your own awesome sound effects on Online Sequencer!

Examples

Here are some sound effects that I drew inspiration from, or just think are amazing.

More Examples

Here are some sound effects that I made.