Squeezed vacuum with large photon numbers is an example of a macroscopic system with nonclassical properties. These properties are manifested in pairwise intensity correlations, also called twin-beam squeezing. We produce squeezed vacuum in a traveling-wave pulse-pumped frequency non-degenerate optical parametric amplifier (NOPA). Twin-beam squeezing is measured via direct detection and measurement of the difference-signal variance for two balanced detectors. It is shown that the study of the intensity correlations using this method requires a collection of a large number of modes, both longitudinal and transverse.