twinmind / sm-808

Programming exercise - code the sequencer part of a Drum Machine

SM-808 Practice exercise

The goal of this exercise is to practice designing models and interfaces.

There aren't good or bad solutions, there are solutions that match the requirements and some that don't. There are solutions that might be considered elegant by some and solutions that would be considered clever.

Building a Drum Machine

This exercise assumes you are somewhat familiar with drum machines. If you aren't please read http://en.wikipedia.org/wiki/Drum_machine

Your challenge is to code the sequencer part of our Drum Machine which we called SM-808. More precisely you will need to sequence and "play" your own version of the famous four-on-the-floor rythm pattern.

Note that instead of hearing an actual sound, you are expected to generate a real time visual representation of the sequence being played.

Expected output

Here is some pseudo code showing the expected interaction and one way to represent the output (you are encouraged to find a better way).

You can use a command line output, work in the browser or use an electric circuit.

Use whatever programming language you want, as long as we can execute your solution.

// create a new song
song = Song -> bpm: 128, title: Animal Rights

// add the 3 patterns
song <- Kick   |X|_|_|_|X|_|_|_|
song <- Snare  |_|_|_|_|X|_|_|_|
song <- HiHat  |_|_|X|_|_|_|X|_|

song.play

// -> real time output
// |Kick|_|HiHat|_|Kick+Snare|_|HiHat|_|Kick|_|HiHat|.....

(ignore the audio outputs print at the beginning but pay attention to the output speed at a BPM of 128)

Extra info

• A song contains multiple patterns being sequenced for different samples.
• A song plays at a given tempo (AKA bpm), the tempo does not need to be able change while the song plays.
• For this exercise, you are expected to implement 3 patterns for the following sounds/samples: kick, snare and hihat (you can use the example pattern or come up with your own).
• The time signature is expected to be 4/4 (if you don't know what that is, don't worry and ignore this instruction).
• The pattern is expected to be 8 steps or more.
• Your code will be executed on the command line or in the browser.
• Try to keep external dependencies to a minimum.
• See next section to see what to output.
• The output isn't expected to be in sync with the tempo/BPM, but if you'd like to do so, go for it!

Timing information

Outputting the patterns in tempo isn't required for this exercise, but if you wish to do so you might need some extra information.

At a 4/4 time signature of 60 BPM (beats per minute), we get 1 beat per second. We can assume that 8 steps = 1 bar, representing 4 beats.

In other words, a 8 step pattern would take (60/BPM)*4 seconds to play and each step would take ((60/BPM)*4)/8 seconds.

If you're having fun

If you're submitting this exercise to apply for a job at Splice, please know that under no circumstances are any of these things expected or required. These are just some ideas for extending your work, if you're having fun with the project!

• Try mixing and matching patterns of different durations (8, 16, 32 steps), note that if you have 2 patterns, one 8 and one 16, the 8 should play twice while the 16 plays once.
• Add support for velocity (the amplitude/volume of a note).
• Try to output sound (macOS has the say command, Windows has ptts, also most language have bindings for portaudio

If you can't stop:

• How about live play? Can you allow users to add/remove/change patterns while playing?
• Make it even more interactive and add a web interface/GUI!

Splice Evaluation

If you are given this exercise as a code challenge, we are going to anonymize your submission and evaluate it using a rubric. There is no specific language requirement for the submission. Please use the language with which you are most comfortable working, as we'd like to see how you'd approach something when working with familiar tools. Provided things look good, we'll set up a time to meet with two backend engineers to chat about the approach you took, and answer any questions you may have.

So that you're prepared, here is an overview of the things we'll be evaluating and discussing about your submission:

• How much time did you spend on the exercise? What parts took longer?
• What were the hard parts, and what parts did you enjoy most?
• How thoroughly is the submission documented?
• How well is the submission tested?
• How clearly are the key concepts modeled?
• What kinds of trade-offs were made in balancing simplicity and flexibility? Can your solution be easily extended to support a change in requirements?
• Is the code written in a readable and consistent style, such that someone familiar with the language would understand what you're doing easily?

Submit your solution

If you want your solution to be reviewed you can:

• email the hiring manager your implementation as a zip or link to your repo (for candidates we are interviewing only)
• fork this repo and send a PR (community reviewed)
• create an issue with the url for your implementation (community reviewed)