Signal processing techniques are essential for accurately converting continuous signals to digital formats and vice versa. When a continuous signal is sampled with a period T, the resulting sampled signal exhibits replicas of the original spectrum in the frequency domain, spaced at intervals equal to the sampling frequency. To handle this sampled signal, a zero-order hold method can be applied, which creates a piecewise constant signal by retaining each sample's value until the next sampling period.

In the frequency domain, the zero-order hold modifies the signal by introducing a sinc function due to its Fourier transform. This sinc function modulates the amplitude of the spectral replicas, attenuating them. Despite this modulation, the sampled signal still requires further processing to smooth out the resulting waveform.

Convolution of the sampled signal with a triangular impulse response further refines the signal. This convolution operation results in a time-domain signal that is smoother and free of abrupt peaks. In the frequency domain, this process smooths the central portion of the curve and compresses the side replicas more effectively than the zero-order hold alone, reducing unwanted spectral components.

For optimal signal reconstruction, an ideal low-pass filter is employed. This filter removes all spectral replicas, allowing only the original spectrum to pass through. The ideal filter's time-domain impulse response is characterized by a sinc function, which, when convolved with the sampled signal, produces a smooth and continuous time-domain signal.

This method, known as band-limited interpolation, ensures that the reconstructed signal closely approximates the original continuous signal. By carefully filtering the sampled signal and utilizing the sinc function's properties, band-limited interpolation minimizes distortion and artifacts, thereby achieving accurate signal reconstruction. This process is critical in applications such as digital audio and communication systems, where maintaining signal integrity during digital-to-analog conversion is essential for preserving the quality and fidelity of the original signal.