Why use a Lookup Table in DSP?

Lookup tables (LUTs) replace expensive mathematical operations (like sin, cos, log) with pre-computed array accesses. This significantly reduces CPU cycles, which is critical for real-time processing on microcontrollers.

What is Q15 and Q31 format?

Q15 and Q31 are fixed-point number formats used in DSP to represent fractional numbers using integers. Q15 represents values between -1 and ~1 using 16-bit integers, while Q31 uses 32-bit integers for higher precision.

DSP Lookup Table Calculator | Waveform & LUT Generator

Table Configuration

Function Type

Points (Size)

Output Data Type

Input Start (x)

Input End (x)

For Sine: 0 to 2π ≈ 6.28318

Amplitude / Scale

Output multiplier (e.g., DAC max vol)

Y-Offset

Shift curve up/down

Variable Name

Format Style

Preview & Code

About this Tool

The DSP Lookup Table Calculator is a professional engineering utility designed for developers working with embedded systems (Arduino, STM32, ESP32, FPGA) and digital signal processing.

Real-time mathematical operations like `sin()`, `cos()`, or `log()` are computationally expensive. In time-critical applications—such as audio synthesis, motor control, or FFT (Fast Fourier Transform)—these operations can cause bottlenecks.

A Lookup Table (LUT) solves this by pre-computing the values and storing them in an array. The processor simply "looks up" the value by index, which is hundreds of times faster than calculating it.

Key Features

Fixed-Point Support: Q15 (Int16) and Q31 (Int32) formats for processors without Floating Point Units (FPU).
Window Functions: Generate Hamming, Hanning, and Blackman windows for filter design and FFT.
Instant Visualization: See your waveform before you implement it.
Multi-Language Export: Get ready-to-paste code for C, C++, Python, and more.

How to Use

Select your Function Type (e.g., Sine for audio generation).
Choose the Table Size (Points). Larger tables = higher precision but more memory usage. A power of 2 (256, 1024) is recommended for efficient bit-masking.
Set your Data Type. Use `Float` for modern MCUs, or `Int16` (Q15) for older or low-power chips.
Adjust Amplitude to maximize dynamic range (e.g., scaling to 32767 for Int16).
Copy the code array into your project source file.

Frequently Asked Questions

What is the advantage of using a LUT? +

Speed. A memory access takes a few cycles, while a `sin()` calculation involving Taylor series expansion can take hundreds. It also ensures deterministic timing, which is crucial for real-time OS (RTOS) tasks.

How do I use a Q15 Fixed Point table? +

A Q15 number represents fractional values from -1 to 0.999. It maps 1.0 to 32767. To use it: `float result = (float)lut_value / 32768.0f;`. In integer math, you perform operations and then bit-shift right by 15 to normalize the result.

Does size matter? (256 vs 1024) +

Yes. A 256-point sine table usually has enough precision for basic control loops or 8-bit audio. For high-fidelity audio or precise motor control, 1024 or 4096 points are preferred. Use Linear Interpolation between points to get high precision even with small tables.

Copied to clipboard!

Read Also: