Launch your digital audio workstation and import the audio tracks you plan to modify. Before you can begin altering the sonic characteristics of your track, you will need to eliminate any noticeable peaks in volume as well as any abrasive hisses. If you are recording vocal tracks, carefully analyze the wave form and take note of any significant visual spikes in the wave. Listen back to this section of track and lower the volume of the track slightly when the peak occurs. By "flattening" your audio, you can improve the results of other audio processes such as equalization and compression.
Lower the volume level of high range frequencies (2.4 khz to 14.4 khz) in your track using a graphic equalizer. If you have a hardware-based equalizer, lower the small dials in this frequency range. If you are using digital tools, assign a graphic equalizer to individual tracks or your entire mix and reduce the volume in the designated frequency range. Analog tape recorders typically lose high-range frequencies during the recording process. Reduce these frequencies with your digital recorder and your mix will begin to assume the characteristics of older productions.
Raise the upper mid-range frequencies (1 to 2.4 khz) in your equalizer to add richness to your instrumental lines and vocal tracks. Augmenting these frequencies will increase the presence of your accompanying tracks such as rhythm guitar and backing vocals. Place these tracks in the "front" of the mix to add the denser quality to your production often associated with vintage recordings.
Use a hardware or software-based compressor to boost the volume level of your tracks and reduce the presence of remaining high-range frequencies or hisses. Compression will balance the volume levels of your overall mix, removing any gains or reduction in volume that may inadvertently occur due to wave frequency cancellation or recording discrepancies.
Purchase a warming plug-in such as PSP Vintage Warmer or Nomad Factory's Tube Warmer to add a simulated analog saturation to your mix. These products are available for download from the manufacturer. Although these plug-ins are moderately expensive, they will produce outstanding results. After downloading, follow the steps provided to activate your new plug-in.