The song controls are located in the top left corner of the screen.
The top button shows the audio engine load in %. When the load is 100% or more, the audio engine is overloaded and cannot produce sound quickly enough and will sound staticy or stutter. This means there are too many notes (and voices) being played at the same time or the instruments are too complex. To remedy this, either reduce the number of notes being played (across all instruments) when the load goes above 100% or reduce the complexity of one or more instruments.
The load indicator is also the button to switch between the synthesizer screen and the sequencer screen.
Below the load indicator button is the Play button to continue playing the current sequence starting at the current block. Beside it is the Loop button that plays the current block repeatedly without advancing to the next block in the sequence.
Below the Play button and Loop button is the STOP! Button. This stops the current sequence and also clears all audio buffers. This can be useful when a filter setting or modulator setting has produced a sound out of range and changing parameters does not appear to work.
To the right of the load indicator are the current block number and the total number of blocks in the sequence. Beside this is the current line number. And beside this are the current polyphony of the selected instrument and the total polyphony of all the instruments. In the top right corner of the screen is the filename of the current song.