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Time stretching/pitch shifting without DSP, possible or not?
bennetng
post Sep 18 2012, 10:47
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I mean time stretching without changing pitch and pitch shifting without changing speed.

I ask this because my friend recently purchased a turntable (Stanton ST150) and it has time stretch function.

http://www.stantondj.com/pdf/products/turn...t150_manual.pdf

The manual says

QUOTE
Note: This turntable has separate analog and digital circuits. If you are
looking for a purely analog signal, use the Phono output. For access to
the Key correction feature use the Line output or S/P DIF output.


QUOTE
Note: Key lock and Digital output
processing is only available when the LINE
output is used.


So from my common sense and English level (not my native language), the line out is in fact converted from digital. But my friend insisted on thinking that the processing is done in analog domain and said if EQ can be done in analog domain, why time stretching/ pitch shifting can't?

What is your opinion?
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dumdidum
post Sep 18 2012, 11:01
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this is def done digitally.

the point is, many DJs have not the slightest clue about digital audio. almost universally, they think of a lot of gear as analog which is, in fact, digital.

example: when DJs discuss stand-alone DJ mixers from pioneer, denon, rane, behringer, etc., they think of these as analog mixers. which is ridiculous, given all of these companies have switched to producing digital mixers years ago. some of those mixers even have a block diagram in their manual which clearly shows the AD and DA stages. but people are still fully convinced that the gear is analog and will sound better than mixing in a software that's controlled via midi.

i imagine the same is going on with turntables which are all "analog" even if they got S/PDIF or USB. it's probably not worth your time arguing with those people..

This post has been edited by dumdidum: Sep 18 2012, 11:02
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bennetng
post Sep 18 2012, 14:14
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QUOTE
but people are still fully convinced that the gear is analog and will sound better


Actually he said analog sounds much better than digital while listening through line out...

This post has been edited by bennetng: Sep 18 2012, 14:15
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dumdidum
post Sep 18 2012, 15:52
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QUOTE (bennetng @ Sep 18 2012, 15:14) *
QUOTE
but people are still fully convinced that the gear is analog and will sound better


Actually he said analog sounds much better than digital while listening through line out...

the st-150 and str8-150 have two outputs, stereo RCA and s/pdif. there is a switch which allows you to select whether the RCAs output line-level or phono level.

when that switch is set to phono, the unit functions as nothing but a normal analog TT. no digital signal processing is going on, there is no amplification. when you set the switch to line, the signal goes through a phono preamp and time stretching may be applied.

iirc (but it's been a while since i've played with one of these), when using s/pdif, the "key lock" button also functions just as when using RCA and having the switch set to "line" (as opposed to "phono").

EDIT: i realize my posts don't really live up to the standard of the "scientific discussion" forum. i just wanted to say that (i) the st-150 indeed does time stretching digitally** and (ii) i don't think there is much value in having a discussion about the fidelity of "analog" sound with most DJs.

---

** in fact, stanton advertises the unit as the ST.150 Digital Turntable.

This post has been edited by dumdidum: Sep 18 2012, 16:03
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mzil
post Sep 18 2012, 16:43
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It is possible to do analog pitch shifting although I doubt any TT on the market does.
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bennetng
post Sep 18 2012, 17:06
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So are there any dedicated analog machines doing that? I would like to hear the result because recent DSP solutions such as DAWs, VST plugins and soundcard DSPs' Time stretching/pitch shifting quality still not very good. (Melodyne, Dirac, Elastique, Radius, Soundtouch, Creative's hardware DSP...)
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pdq
post Sep 18 2012, 17:26
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QUOTE (mzil @ Sep 18 2012, 11:43) *
It is possible to do analog pitch shifting although I doubt any TT on the market does.

Analog pitch shifting without time stretching? Are you sure about that? Do you have a link?
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dumdidum
post Sep 18 2012, 17:42
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QUOTE (pdq @ Sep 18 2012, 18:26) *
QUOTE (mzil @ Sep 18 2012, 11:43) *
It is possible to do analog pitch shifting although I doubt any TT on the market does.

Analog pitch shifting without time stretching? Are you sure about that? Do you have a link?
http://en.wikipedia.org/wiki/Pitch_shift " It could be accomplished on an early reel-to-reel tape recorder by changing the diameter of the capstan drive shaft, or using a different motor."

This post has been edited by dumdidum: Sep 18 2012, 17:43
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benski
post Sep 18 2012, 17:49
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QUOTE (pdq @ Sep 18 2012, 12:26) *
QUOTE (mzil @ Sep 18 2012, 11:43) *
It is possible to do analog pitch shifting although I doubt any TT on the market does.

Analog pitch shifting without time stretching? Are you sure about that? Do you have a link?


There are a number of analog devices that do something similar, but the process is better known as Frequency Shifting. Notable, it shifts all frequency by a fixed amount, which destroys the harmonic relationship present in musical content. Digital-Style pitchshifting could potentially be done in the analog realm with a filterbank (acting as an FFT) and a corresponding bank of BBDs or tape loops.
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benski
post Sep 18 2012, 17:50
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QUOTE (dumdidum @ Sep 18 2012, 12:42) *
QUOTE (pdq @ Sep 18 2012, 18:26) *

Analog pitch shifting without time stretching? Are you sure about that? Do you have a link?
http://en.wikipedia.org/wiki/Pitch_shift " It could be accomplished on an early reel-to-reel tape recorder by changing the diameter of the capstan drive shaft, or using a different motor."


This time-stretches as well
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pdq
post Sep 18 2012, 17:56
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QUOTE (benski @ Sep 18 2012, 12:49) *
There are a number of analog devices that do something similar, but the process is better known as Frequency Shifting. Notable, it shifts all frequency by a fixed amount, which destroys the harmonic relationship present in musical content.

I assume this would give you the "Donald Duck" effect, as when to decode single sideband with a carrier that is slightly off in frequency.
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greynol
post Sep 18 2012, 18:15
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QUOTE (bennetng @ Sep 18 2012, 06:14) *
QUOTE
but people are still fully convinced that the gear is analog and will sound better


Actually he said analog sounds much better than digital while listening through line out...

This is what I like to call a TOS #8 violation by proxy. Please refrain from posting unsubstantiated 3rd party subjective anecdotes. Let your friend contribute directly.

Also, does this topic really have to turn into another placebophile debate? I don't see how introducing a referendum on the knowledge of DJs is even remotely useful.


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bennetng
post Sep 18 2012, 18:26
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QUOTE (greynol @ Sep 19 2012, 01:15) *
QUOTE (bennetng @ Sep 18 2012, 06:14) *
QUOTE
but people are still fully convinced that the gear is analog and will sound better


Actually he said analog sounds much better than digital while listening through line out...

This is what I like to call a TOS #8 violation by proxy. Please refrain from posting unsubstantiated 3rd party subjective anecdotes. Let your friend contribute directly.

Also, does this topic really have to turn into another placebophile debate? I don't see how introducing a referendum on the knowledge of DJs is even remotely useful.


Please don't be so sensitive. I said this because I *don't* agree with my friend. The discussion is talking about I suspect the line out (not phono out) of that turntable is actually converted from digital.

This post has been edited by bennetng: Sep 18 2012, 18:38
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greynol
post Sep 18 2012, 18:37
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QUOTE (bennetng @ Sep 18 2012, 10:26) *
Please don't be so sensitive. I said this because I *don't* agree with him. The discussion is talking about I suspect the line out (not phono out) of that turntable is actually converted from digital.

I understand, but I still don't find it either necessary or constructive. The merits can be argued without it. FWIW, the second part of my post wasn't directed at you.

This post has been edited by greynol: Sep 18 2012, 18:38


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mzil
post Sep 18 2012, 18:57
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QUOTE (benski @ Sep 18 2012, 12:50) *
QUOTE (dumdidum @ Sep 18 2012, 12:42) *
QUOTE (pdq @ Sep 18 2012, 18:26) *

Analog pitch shifting without time stretching? Are you sure about that? Do you have a link?
http://en.wikipedia.org/wiki/Pitch_shift " It could be accomplished on an early reel-to-reel tape recorder by changing the diameter of the capstan drive shaft, or using a different motor."


This time-stretches as well


I owned a pitch shifter in the 70's(?) or 80's that was fully electronic and had no reliance on tape transport and didn't time stretch. Although Lexicon and Eventide now do digital stuff, back then their processors like the Harmonizer H910 and the Lexicon Varispeech (c. early 1970's) were analog. [Mine was on a bread board my father built, but I think it was the same circuitry.] [edit to add: Oops, I guess it was digital. My bad. I owned it so many years before CD I just assumed it was analog!]

I owned a VCR which could play at double speed with "Chipmunks" audio, at the time. I would connect its output to the pitch shifter and corrected the pitch, but of course maintained the fast speed. I remember that I was able to watch/hear a one hour news program or talk show in only 20 minutes or so (that included fast forwarding through the commercials). I was the only person I knew of who thought to do this. Keep in mind this was decades before Tivos and other DVRs were on the scene.

This post has been edited by mzil: Sep 18 2012, 19:15
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John_Siau
post Sep 18 2012, 19:36
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I seem to recall that there were analog frequency-shift devices that were built with "Bucket Brigade Devices" (BBDs). A BBD device passes a charge down a long string of switched capacitors, and can be used as an analog audio delay line. These BBD frequency-shift devices were sampled analog systems, and not digital.

The BBD would be loaded with a short segment of audio, and then played back at at different shift rate. The segments of audio were simply spliced together by repeating or omitting chopped segments. These systems could frequency shift, but could not time stretch.

In many cases, time stretching was accomplished by using a tape recorder, and the frequency-shift device was used to restore a normal pitch.


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mzil
post Sep 18 2012, 19:44
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A 1968 example of the tape based "Electro Rate Changer" (with time stretching):
http://www.youtube.com/watch?v=c8N72t7aScY#t=3m

The song chosen might have been a nod to the people working on early synthetic speech, who used the same song.
http://www.youtube.com/watch?v=41U78QP8nBk

This post has been edited by mzil: Sep 18 2012, 19:52
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John_Siau
post Sep 18 2012, 19:47
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Here is a link to an old BBD data sheet from 1975. The device is a TDA1022. It lists "variable compression and expansion of speech in tape recorders" as an application.

http://www.synthdiy.com/files/2003/TDA1022-b.pdf


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bennetng
post Sep 18 2012, 19:59
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Thanks for the explanations. Then I guess the analog approach is similar to Granular synthesis.
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krabapple
post Sep 19 2012, 17:30
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On a two recent remixes by Steve Wilson (one the 1970 King Crimson track 'Big Top' , one of 1970 Emerson, Lake & Palmer track 'Knife Edge') the original tracks had variable pitch + speed effects, but Wilson's remixes don't.

'Big Top' increases in speed and pitch (it fades out as the musical snippet keeps rising higher and higher, faster and faster)
'Knife Edge' decreases in speed and pitch (it ends with the tape slowing down to a halt)

It seems to me it should have been possible to replicate these effects digitally; I imagine I could do a fair job just using Adobe Audition 1.0's time/pitch tool,and that's hardly current technology. Am I wrong?

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bennetng
post Sep 19 2012, 17:55
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Most samplers/romplers support this kind of pitch shifting (pitch bend/pitch wheel). It is a standard function in General MIDI synthesizers. The default range is +/- 2 semitones. Synthesizers compatible with "pitch wheel sensitivity" command can shift up to something like +/- 1 octave.

Samples are usually looped and the length is controlled by note on/off command so we usually don't notice the changes of speed.
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mzil
post Sep 19 2012, 18:30
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QUOTE (krabapple @ Sep 19 2012, 12:30) *
It seems to me it should have been possible to replicate these effects digitally; I imagine I could do a fair job just using Adobe Audition 1.0's time/pitch tool,and that's hardly current technology. Am I wrong?

Somebody has done a pitch correction on the Beatles' "When I'm 64" using Audition, so I guess it shouldn't be a problem. [At first I didn't really notice the difference until I then compared it to the original version.]

This post has been edited by mzil: Sep 19 2012, 18:34
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greynol
post Sep 19 2012, 18:46
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I don't think pitch correction which also changes playback speed is a problem with competent wave editors. FWIW I did it on the original London release of Between the Buttons and am perfectly happy with the results.


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krabapple
post Sep 19 2012, 20:40
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QUOTE (greynol @ Sep 19 2012, 13:46) *
I don't think pitch correction which also changes playback speed is a problem with competent wave editors. FWIW I did it on the original London release of Between the Buttons and am perfectly happy with the results.



I've just noticed that Audition even has the equivalent of a pitch/speed 'fade' -- continuous pitch/speed bend up or down, with preset limits. So I don't get why Wilson couldn't replicate the original effects on those two tracks I mentioned.
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greynol
post Sep 19 2012, 21:46
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From what I understand of Wilson, he's not exactly objective when it comes to digital audio. On the other hand he does use a Line 6 Pod. wink.gif

This post has been edited by greynol: Sep 20 2012, 01:17
Reason for edit: added link.


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