# Using MFCC and MFCC Delta features with a CNN

A lot of studies feed MFCCs as well as MFCC delta and double deltas directly to a CNN for audio classification. My question is, are the MFCC Deltas concatenated with the MFCC matrix? Most papers simply state they used MFCC + MFCC Delta + MFCC Double Delta and the plus sign is left to interpretation!