Open the top of the gutted piano. Set up your microphone and computer, or a device able to transfer the recording to your computer, so that it is positioned to record from within the opening. Pluck, hit or scrape the wire for test recordings to be sure the equipment is functioning properly, then begin recording.
Scrape the key from approximately the midpoint of any single piano string to where it ends. Scrape the key as smoothly as possible, at a constant medium speed. Repeat multiple times without pause, keeping the timing of each scrape as consistent as possible and avoiding large pauses between scrapes.
Search for a recording of a key-scraped gutted piano string through the Internet or other means in .wav form, if you do not have the ability to perform the above steps due to lack of recording equipment or a gutted piano; if necessary, convert an alternate file type into .wav format.
Import your recording into your computer audio editing program, such as Audacity, ProTools or Logic. This setting is found under the File menu in most programs.
You will notice that your base recording already sounds very similar to the finished TARDIS sound effect. From here on, the specific parameters of the effects used will vary depending on each recording.
Open the FX Mix, usually found with the mixing settings under Tracks or Reverb, and adjust so that the production effects do not overwhelm the base recording.
Select the full audio recording track. Open your audio editor's Reverse function and run it over the entire track. Play it back; if the reverse echo effect created overwhelms, undo the Reverse function and adjust the FX Mix before trying again.
Adjust the delay and/or reverb of the recording, if desired or if the effect so far does not sound full enough. This step is optional but will produce a sound closer to that of the classic TARDIS sounds from earlier in the series.
Select the Bounce function. When the file has finished bouncing, run the Reverse function again as in Step 6.
Adjust the overall pitch of the recording, if necessary, depending on which TARDIS effect you wish to replicate. Open your audio editor's pitch alteration or correction function. Adjust the pitch up or down as desired.
Select the entire audio file and save. Go to the Bounce To or Convert and Save function in your audio editor and run it. Play back your completed, converted audio file to be sure your sound was preserved properly; if not, alter your reverb, delay, FX Mix or pitch settings to compensate, and repeat this step until the final file sounds correct. Save the final file.