I’m converting some commercial cassette recordings to CDs and I’m trying to verify the pitch accuracy of the recordings based on having the actual musical scores. As I don’t know how accurate the original studio equipment was (producers sometimes time-compress to ‘fit’ the recordings into the media) nor trust the absolute accuracy of the TASCAM 302 deck I’m using.
I recorded the cassettes at 24/96 using my new TASCAM DR-40 digital recorder, and uploaded the resulting files into WL7, one file per side of cassette. My strategy is to correct for mechanical anomalies first and performance problems second.
Here is the process so far, and where I ran aground:
I noticed that the left channel was lower than the right one. So I used Process->Change Level->Find Current Peak Level on each channel to determine what the overall level difference was between them. Noting that I then boosted the lower one by the difference so both are relatively equal. Since it is average, any balance issues in the mixdown should still be valid (instrument location on stage).
I selected two passages from two songs where the performers sustained one unison note. #1 was a Flute, #2 was a children’s choir. I created two new audio files and pasted the copied ‘phrases’ into the window. I checked for DC offset (Analysis->Global Analysis-> Estras-> Find DC Offset) and found it was 10db for one and 14 db for the other. So, each recording is offset and will need to be corrected separately.
Having corrected the DC offset, I then looked at the pitch of the single tones. There appears to be two places to get this information. Analysis->Global Analysis->Pitch Tab which provides the average pitch of the left and right channels (Even when only one channel is being analyzed !!! ) and they are different even with this sample of a single tone…(F#5 and D#5)… The second choice is Process->Pitch Correction->Find current pitch of audio selection (E1). Since it is E1/-16cents I chose to ‘correct’ it for this note. When I select the pitch E1 and have it calculate the correction it comes up +16 as expected (auto/preview, best, correct formants, Modulate formants correction). When I check the pitch again, using the same tool, it tells me E1 +2 cents. I can go -2 and it will be E1 -1 cent, etc. It does everything but land right on 0 cents … Why?
Am I correct in assuming that I can determine the pitch difference (i.e. +16) and just apply it to the entire file to correct the overall pitch variance from the cassette speed differences? Or does this kind of variation usually go all over the place depending on the skill of the performers and trying to correct it universally is a waste of time?
What is the difference between the Pitch Correction analysis, the Global Analysis Pitch tab, and the Pitch Quantizing choice under Process? Which should be used where?
I also noticed that artifacts accumulate if you correct the pitch up and down 1 cent repeatedly. The effect is a percussive effect at the start of the sample. Why? It seems to me that this should be simple addition/subtraction of numbers from the frequencies.
What should I be doing instead? I tried this approach because I know I have voice recordings from old radio programs/dramas that are recorded at incorrect speeds and need correction as well. So, I need to understand the preferred process.
Thanks in advance for you help.