Questions about approach for background music generation for songs

Question

I have a project proposal for music lovers who have no knowledge in audio processing. I think the project is interesting, but I don't have clear picture on how to implement it.

The project proposal: Some people like singing, but they cannot find appropriate musical accompaniment (background music). People who can play guitar, they may sing with playing guitar (the rhythm provided by guitar is background music). The project is to achieve the similar result like playing guitar for people singing.

I think to implement this project, the following components are required:

1. Musical knowledge (how guitar plays as background music (maybe simple pattern will work))

2. signal/audio processing

   • Key detection
   • Beat detection
   • Chord matching

Is there any other component I missed to achieve my purpose? Any libraries can help me? The project is supposed to be completed in 1.5 month. Is it possible? (I just expect it to work like guitar beginners playing background music). For development languages, I will not use c/c++. Currently my favorite is python, but possibly use other programming language as long as it can help simplify the implementation process.

I have no musical background and just studies very basic audio processing. Any suggestions or comments are apprietiated.

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Edited Information: I tried to search auto accompaniment, and there are some software. I didn't find any open source project for it, I want to know the details on how it process audio information. If you know any open source project about it , please share your knowledge, thank you.

Answer 1

You might start by considering what a guitarist would have to do to successfully accompany a singer singing in a situation where that they have no prior knowledge of the key, chord progression, or rhythm of the song (not to mention its structure, style, etc.)

Doing this in real-time in a situation where the accompanist (human or computer) has not heard the song before will be difficult, as it will take some time to analyse what's being sung in order to make appropriate musical choices about the accompaniment. A guitarist or other musician having this ability in the real world would be considered highly skilled.

It sounds like a very challenging project for 1.5 months if you have no musical background. 'maybe simple pattern will work' - maybe, but there are a huge number of simple patterns possible!

Less ambitious projects might be:

• record a whole song and analyse it, then render a backing (still a lot of work!)
• to create a single harmony line or part, in the same way that vocal harmoniser effects do
• generating a backing based on a chord progression input by the user

Edit in reply to your first comment:

If you wanted to generate a full accompaniment, you will need to (as you say) deal with both the key and chord progression, and the timing (including time signature and detecting which beat of the bar is 'beat 1')

Getting this level of timing information this may be difficult, as beat detection from voice only is not going to be possible using the standard techniques used to get beat from a song (looking for amplitude peaks in certain frequency ranges).

You might still get good results by not caculating timing at all, and simply playing your chords in time with the start of the sung notes (or a subset of them).

All you would then need to do is

• detect the notes. This post is about detecting pitch in python: Python frequency detection. Amplitude detection is more straightforward.
• come up with an algorithm for working out the root note of the piece (and - more ambitiously - places where it changes). In some cases it may be hard to discern from the melody alone. You could start by assuming that the first note or most common note is the root.
• come up with an algorithm for generating a chord progression (do a web search for 'harmonising a melody'). Obviously there is no objectively right or wrong way to do this and you will likely only be able to do this convincingly for a limited range of styles. You might want to start by assuming a limited subset of chords, e.g. I, IV, V. These should work on most simple 'nursery rhyme' style tunes.

Of course if you limit yourself to simple tunes that start on beat one, you might have an easier time working out the time signature. In general I think your route to success will be to try to deal with the easy cases first and then build on that.