reproduce sounds from assets subfolder

I have some sounds into a subfolder of assets folder, named audio, and i need to reproduce it. Each sound filename (for now is a .waw files, but later they will become an .mp3) is stored into an array. This is code that i use to reproduce sound:

 AssetFileDescriptor descriptor = null;
        MediaPlayer player = new MediaPlayer();
        try {
            descriptor = context.getAssets().openFd("/audio/"+sounds[Integer.valueOf(v.getTag().toString())]);
            player.setDataSource(descriptor.getFileDescriptor(), descriptor.getStartOffset(), descriptor.getLength());
            descriptor.close();

            player.prepare();
            player.setVolume(1f, 1f);

            player.start();
        } catch (IOException e) {
            e.printStackTrace();
        }

but i obtain a FileNotFoundException wher i call openFd method. How can i solve this issue?