In my opinion, with the calculation process, SNR can vary from 0 to ∞.

The minimum and maximum signal-to-noise ratio (SNR) for ECG signals can vary significantly depending on various factors such as:

Minimum SNR:

• Noise source: Different noise sources (e.g., muscle artifacts, power line interference, baseline wander) can have varying levels of intensity.
• Recording environment: Factors like electromagnetic interference, patient movement, and electrode quality can affect the noise level.
• Recording equipment: The sensitivity and noise characteristics of the ECG device can influence the SNR.

Maximum SNR:

• Signal amplitude: A stronger ECG signal can have a higher SNR compared to a weaker one.
• Noise reduction techniques: The use of filtering, noise cancellation algorithms, or other signal processing methods can improve the SNR. 1. Improved Noise Cancelling Algorithm for Electrocardiogram Based on Moving Average Adaptive Filter - MDPI www.mdpi.com📷

General ranges:

• Minimum SNR: Typically, a minimum SNR of around 5 dB is considered necessary for reliable ECG analysis. However, this can vary depending on the specific application and noise conditions.
• Maximum SNR: In ideal conditions with minimal noise and a strong ECG signal, the SNR can reach 40 dB or higher.