[78-L] PItch change

[DAVID BURNHAM]

I don't usually quote from such a long letter but this issue was discussed over a week ago and any comments I make won't make any sense without the comment which inspired the response.

I found this posting a little disturbing because it demonstrated some rather narrow thinking on the part of someone who obviously has a broad understanding of his specialty.

From: DAVID BURNHAM <burnhamd at rogers.com>
> Michael, I assume you work with Digital Audio Workstations, (DAWs),

Rarely.  Actually, I work more with REAL equipment, which has a heritage
and a set of terminology which existed before the computer and before
the geeks who design the DAW programs were even born.  These terms,
including "Pitch Shifting" were originated before computers were
invented.  I use pitch shifters that are not attached to a computer.  I
use turntables with speed controls that are not attached to a computer. 
I use tape recorders with variable speed controls that are not attached
to a computer.  I do these operations BEFORE feeding the signal into the
computer because some of these operations, as you state: "if it done to
any extent [in the computer], usually introduces undesireable audio
artifacts."

~~~~~~~~~~~~~~~~~~~

DAWs are REAL equipment!  They have been designed by engineers as the continuing evolution of recording technologies.  To imply, as you do above and in the section below, that these systems are designed by geeks who don't know the first thing about the development of audio equipment is insulting, demeaning, disparaging and wrong.  Digital technology has perfected many systems which, though they had a counterpart in analog days, they were far from perfect.  

Anyone who has worked with a pre-digital reverb unit knows that they sound like exactly what they were - springs or plates stimulated into mechanical activity by feeding them with sound waves.  Modern digital reverb units can accurately reproduce the ambience of the finest concert halls in the world as if the performance were being recorded in those environments.  


An analog filter was pretty useless beyond 2nd or 3rd order.  If you wanted to remove a rumble which was around 30hz or lower, you had to start rolling off around 200 hz to get rid of it.  With digital filters, you can have flat response down to 35 hz and with a brick wall filter, remove everything below 30.

Digital recordings are ruler flat across their useful band width.  They have no low frequency limitation whatsoever and by using sufficiently high sampling rates, can extend the high frequency limits up to over 100khz.  Analog tape recorders have a useful band of 10 octaves - a situation where the high frequency limit is 1000 times the low frequency limit, (e.g. 20 - 20,000 hz).  This band may be flat within +/- 3 dB.  Any setting up of an analog tape recorder calls for compromises.  When adjusting the record bias, you have to find the best compromise between frequency response, signal to noise ratio and distortion.  No one setting will have these three characteristics optimized.  The best signal to noise you can expect is around 60dB.  However, most of these short-comings are more measureable than audible.  As we know, the finest analog recordings have a quality which is still a treat to the ears.

Certainly digital audio didn't appear on the market completely polished.  The first CDs had a glassy harsh sound which many listeners found unpleasant and caused them to stay married to their LP collections.  However, great strides have been made since the late 70s and the best modern digital recordings are unrivaled.  DSD, (direct stream digital), boasts a frequency response of 0-100khz, a signal to noise range of 135 dB and distortion which is almost unmeasurable.  All analog tape recordings have a certain amount of flutter, and all analog disc recordings have a certain amount of "wow".  These distortions are, and always have been absent from digital recordings.   Any copying of an analog recording introduces "generation losses" - added frequency response errors, distortion and increased noise.  Digital recordings can be copied without any losses whatsoever, (and this has gone a long way towards killing the audio industry).

Single-ended analog noise reduction systems were very unsatisfactory, any noise improvement was more than overwhelmed by the artifacts and signal degradation which they introduced.  Modern digital systems such as CEDAR, in the right hands, can seem to lift the music right out of the noise bed and present it seemingly unaffected.  (Dolby-A systems were very good too but they were double-ended - the signal was encoded, recorded, played back and decoded.

The engineers who developed these digital recording techniques knew exactly what they were doing.  They were completely familiar with the strengths and weaknesses of analog recording and set about perfecting the procedures.  They couldn't have done this without knowing what analog equipment could do.  For instance, another plug-in on many DAWs is a "flanger";  I know a number of engineers who use this effect but have no idea where the word came from.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Michael Biel wrote:
>> This is the problem with the terminology again.  You can't just pitch
>> shift.  You have to speed adjust.  The term "pitch shifting" was coined
>> to mean changing the pitch without changing the tempo. 

> any professional DAW has a plug-in called a "Pitch shifter", and any pitch shifter
> has a setting which allows it to adjust tempo along with the pitch, (like speeding
> up an analog tape), or change the pitch without changing the tempo, (which if it's
> done to any extent, usually introduces undesireable audio artifacts). 

That was exactly my point.  The change in the terminology allows for a
misunderstanding of what is needed, and that happened in this case.  If
you adjust ONLY the pitch, that will not correct the problem of the
original question.  The pitch and tempo must be LOCKED together, and
that is not an inherent understanding if the only the word "pitch" is
used.  Because the word "speed" had a 100 year history of meaning just
that -- the simultaneous adjusting of the pitch and tempo -- it would be
helpful if "speed" would be used to describe this function, leaving
pitch to mean adjusting only the pitch, and tempo meaning adjusting only
the tempo.  The terms were changed by geeks who did not know much beyond
computers and did not adequately think things through. 

Let me explain how the problem arose.  Most of the geeks who designed
computer programs and computer-based recorders had never used a
turntable or a tape recorder.  Those were old fashioned and obsolete.  

(NONSENSE)

So their concept of "speed" only meant how fast their computer
processors could pass bits (or possibly the drugs they used to allow
them to stay up endless hours to meet production deadlines). 

Variable speed turntables go back to the Berliner days of the 1890s,
and for 100 years turntables and variable speed tape recorders had a
control called "Speed".  Not "pitch".  Not "tempo".  SPEED.  It was well
known that adjusting the speed of a turntable or tape recorder would
adjust the pitch of the sound.  It was well known that adjusting the
speed of a turntable would also adjust the tempo of the sound.  But for
some reason every turntable or tape recorder ever made only had a
control marked "SPEED" -- at least till the geeks took over. 

The term Pitch Shifter originated before the first DAW, and was adapted
by the geeks who didn't quite know what the earlier devices actually
did.  As I mentioned in an earlier posting, there were tape oriented
pitch shifters going back to 1935, and the first all-electronic pitch
shifter was the Eventide Harmonizer which was introduced around 1972. 
These operated independent of any recording device, and shifted the
pitch up or down of a live performance or of the playback of a recorder.
Obviously there was no time expansion or compression possible with live
performances -- the tempo remained the same -- but if the source was a
recording, there was a way of adjusting the tempo of the recording by
changing the "speed" of the playback and then using the pitch shifter to
RESTORE the original pitch.  Thus, that was TEMPO SHIFTING.  

So probably without realizing that there had been a 100 year history of
using a "speed" adjustment which would change the pitch and tempo of a
recording, and a fifty year history of using "pitch shifting" to mean
the changing of the pitch without changing the tempo, and "tempo
shifting" to mean the changing of the tempo without changing the pitch,
they dropped the name of the "speed" control and started to instead call
it "pitch shifting"..  

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Looking around my room here, I have five turntables, three of which pre-date digital, and one reel - to - reel tape machine and they all have a controll which says "pitch", they also have a controll which says "speed" - referring to the one which sets 33/45/78 and 7 1/2 or 15 i.p.s.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~





> Obviously, in the case of a constant velocity disc recording, (and I
realize constant velocity can have an entirely different meaning when
applied to equalization), you will want the pitch and tempo to change
together to compensate for the situation on the record when played at
constant speed - where the pitch and tempo will lower as the record is
played, (if from the outside in).  db

This is the real conundrum -- does the recording need to be speeded up
or slowed down!  It depends on what speed you played it at as well as
whether it is a center or rim start.  Let's assume that the World is a
rim-start disc.  The original questioner later in the discussion
mentioned that he had played the record at 33.  Thus as the record
continued to play it will sound like it was slowing down because it had
been speeded up when it was recorded.  Thus the computer must gradually
speed UP the recording.  BUT, what if he had played it at 78?  It would
start too fast and seem to slow down while playing it back because the
record would continue to approach the playback speed of the end of the
recording.  Thus, the computer will have to initially slow down the
recording but gradually reduce the amount of the speed reduction.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is just confusing, and I'm sure if Michael thought about it he would realize that.  It doesn't matter what speed you play the disc at, if it's a rim start, the pitch will decrease as the disc is played and the computer must increase the speed as it reads the file.  Modern pitch-shifting plug-ins can do that.

db