Timing and Sleep

Music exists in time. In Sonic Pi, we control time with sleep and use_bpm.

Setting the Tempo

Every track starts with:

use_bpm 100

BPM = Beats Per Minute. At 100 BPM:

• 1 beat = 0.6 seconds
• 4 beats (1 bar) = 2.4 seconds

Our album ranges from 95-108 BPM:

The Sleep Command

sleep pauses execution for a number of beats:

use_bpm 100

play :c4
sleep 1        # Wait 1 beat (0.6 seconds at 100 BPM)
play :e4
sleep 1
play :g4

Common Sleep Values

sleep 4       # Whole note (1 bar in 4/4)
sleep 2       # Half note
sleep 1       # Quarter note
sleep 0.5     # Eighth note
sleep 0.25    # Sixteenth note

Rhythmic Patterns

Different sleep values create different feels:

# Straight eighths
4.times do
  sample :drum_cymbal_closed
  sleep 0.5
end

# Syncopated
sample :bd_tek; sleep 0.75
sample :bd_tek; sleep 0.25
sample :bd_tek; sleep 1
sample :bd_tek; sleep 1

Loops and Repetition

Simple Loops

4.times do
  sample :bd_tek
  sleep 1
end

This plays 4 kick drums, one per beat.

Infinite Loops

live_loop :drums do
  sample :bd_tek
  sleep 1
end

live_loop runs forever until you stop it. Great for live coding, but we avoid it in composed tracks.

Nested Loops

4.times do                    # 4 bars
  4.times do                  # 4 beats per bar
    sample :drum_cymbal_closed
    sleep 0.5                 # Eighth notes
  end
end

Pattern Timing

A typical 4-beat drum pattern:

define :drums do
  # Beat 1
  sample :bd_tek
  sleep 0.5
  sample :drum_cymbal_closed
  sleep 0.5
  
  # Beat 2
  sample :bd_tek
  sample :sn_dub
  sleep 0.5
  sample :drum_cymbal_closed
  sleep 0.5
  
  # Beat 3
  sample :bd_tek
  sleep 0.5
  sample :drum_cymbal_closed
  sleep 0.5
  
  # Beat 4
  sample :bd_tek
  sample :sn_dub
  sleep 0.5
  sample :drum_cymbal_closed
  sleep 0.5
end

Total sleep: 4 beats = 1 bar.

Timing Math

Always ensure your patterns add up to complete bars:

# Good: adds to 4 beats
define :pattern do
  bass :d2; sleep 0.75
  bass :d2; sleep 0.25
  bass :f2; sleep 1
  bass :d2; sleep 2
  # Total: 0.75 + 0.25 + 1 + 2 = 4 ✓
end

# Bad: adds to 3.5 beats (will drift!)
define :broken_pattern do
  bass :d2; sleep 0.5
  bass :d2; sleep 1
  bass :f2; sleep 1
  bass :d2; sleep 1
  # Total: 3.5 ✗
end

Synchronization

When combining multiple patterns, ensure they align:

# 8 repetitions of 4-beat drums = 32 beats
8.times do
  drums
end

# Must match: 32 beats of bass
8.times do
  bassline  # Also 4 beats each
end

If patterns have different lengths, use least common multiples:

# 3-beat pattern + 4-beat pattern
# LCM(3,4) = 12 beats to sync
4.times { three_beat_pattern }  # 12 beats
3.times { four_beat_pattern }   # 12 beats

Quick Reference

use_bpm 100              # Set tempo

sleep 1                  # Wait 1 beat
sleep 0.5                # Wait half beat
sleep 4                  # Wait 1 bar

4.times do               # Repeat 4 times
  sample :bd_tek
  sleep 1
end

# Beat values at any BPM:
# 4 = whole note (1 bar)
# 2 = half note
# 1 = quarter note
# 0.5 = eighth note
# 0.25 = sixteenth note

Next: Variables and Functions — how to organize and reuse code.