Playgrounds › Noise Schedules › Square Root Schedule

Square Root Schedule

Originating Paper

On the Importance of Noise Scheduling for Diffusion Models

🧑‍🎓 Ting Chen

📍 arXiv 2023

📄 203 citations

Why this schedule?

The square-root schedule front-loads noise more aggressively than the linear schedule but less than exponential approaches. The αˉt\bar\alpha_t curve drops steeply at the beginning—the model is quickly pushed into challenging denoising territory—then gradually levels off as tt approaches TT. This shape prioritizes learning coarse, global structure early while spending more time on the nuanced late-stage transitions. It can be seen as a compromise between the uniform pacing of linear and the delayed-difficulty approach of cosine.

Formula

αˉt=1−t/T\bar\alpha_t = 1 - \sqrt{t/T}
  • •tt = current timestep
  • •TT = total number of timesteps
  • •αˉt=∏i=1tαi\bar\alpha_t = \prod_{i=1}^{t} \alpha_i = cumulative signal retention
normalized values0.000.250.500.751.000.000.250.500.751.00
tt
αˉt\bar\alpha_t1.0000αt\alpha_t1.0000βt\beta_t0.0000SNR\mathrm{SNR}∞

βt\beta_t across all schedules

0.000.250.500.751.000.000.250.500.751.00
LinearCosineSigmoidExponentialCauchyLaplaceSquare RootLogistic

αˉt\bar\alpha_t across all schedules

0.000.250.500.751.000.000.250.500.751.00
LinearCosineSigmoidExponentialCauchyLaplaceSquare RootLogistic