How do you old school playback tape audio at half speed?
Hi
I am working in X3 on digital audio from reel to reel tape recordings.
Some of these recordings off the original master tape are at half speed, some at double speed.
It used to be very easy to double or half the playback speed and the pitch would just follow!
Can someone help guide me in how to do it in X3?
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mettelus
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Re: How do you old school playback tape audio at half speed?
2015/05/29 10:45:30
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Hi and welcome to the forums. The simplest method is to slip-stretch the individual clips (hold CTRL and drag the right edge when see the proper cursor). When completed, for stretches that large, be sure to right click and "Bounce to clips(s)" afterwards to render the audio. The original wav files will remain in your project audio folder if you should need to revisit them at "original speed" later (or you can manually delete them, as desired). Edit: OMG, I really need to cut down on multi-tasking, sheesh... TAPE! See posts below... Adjusting playback sample rate on the file is the best plan of attack (Audacity is the first free one that comes to mind with this capability). More details below.
post edited by mettelus - 2015/05/29 11:56:19
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Beepster
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Re: How do you old school playback tape audio at half speed?
2015/05/29 10:52:03
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☄ Helpfulby mettelus 2015/05/29 11:58:40
Well unfortunately there is no varispeed function right inside Sonar (and many people have been asking for this) but there are more manual ways to go about it.
First though.... why are these recordings at these speeds? Do you not have the playback device or did the person who handed these files to you not realize the speed was wrong when they digitized them? Ideally you would obviously want to digitize at the appropriate playback speed.
However one thing you may want to study up on is the Loop Constructor View. It's too in depth to fully explain in a single post (at least for me) but it has pitch and tempo functions and you can output high quality results (but you really want to do it correctly to acheive that).
The other thing that might work is screwing with the samplerate. As in when you change the samplerate of a project to something other than the samplerate of the audio clip it will act kind of like using different speed settings on a tape machine. In fact this may be your actual problem. The files may have been digitized at a different samplerate than the one you have your project set to. I had this problem with some old files of mine. They were playing all slow and low. I change the project to the correct samplerate and all was well.
Cheers.
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Beepster
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Re: How do you old school playback tape audio at half speed?
2015/05/29 10:54:29
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mettelus
Hi and welcome to the forums. The simplest method is to slip-stretch the individual clips (hold CTRL and drag the right edge when see the proper cursor).
When completed, for stretches that large, be sure to right click and "Bounce to clips(s)" afterwards to render the audio. The original wav files will remain in your project audio folder if you should need to revisit them at "original speed" later (or you can manually delete them, as desired).
That would not deal with the pitch problem unfortunately but that in conjuction with the Transpose process (Process > Transpose) would work. That is of course really manipulating the audio which ideally SHOULD be avoided as much as possible but done correctly Sonar seems to handle quite well. Edit: And just to add to that I think if Varispeed style functions do get introduced I would actually like to see it integrated in the stretch function. Kind of like hold down an extra modifier key when doing the time stretching of the clip and it lower pitch incrementally based on the stretch like slowing down a tape would. And maybe an extra/different modifier could do stuff like gradual speed down/up. aaand just because I'm day dreaming a Pitch/Speed map type thing that you could draw these types of things into (on unison or independent type level) would be soooooper cool.
post edited by Beepster - 2015/05/29 11:07:18
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js516
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Re: How do you old school playback tape audio at half speed?
2015/05/29 11:03:10
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Slip streatch keeps the pitch constant while altering duration. The easiest way to reproduce halfspeed/double speed playback is to record at half /double the intended sample rate, then alter the header of the sample file to the intended sample rate. In other words, if your intended sample rate is 48k and you want to reproduce a halfspeed effect, record at 96khz then use a wav editor (audacity for example) to change sample rate value the header in the wav file to 48khz. When you playback the modified file, it will have twice the duration and half the pitch of the original. Going the other way needs an extra step. Assuming the intended rate is 48khz, recording at 24khz is a bad idea. In that case i would record at 48khz, the modify the rate in the header to 96khz. This modified file will playback at double the pitch and half the duration. The additional step is to downsample the modified file to 48khz to maintain the altered pitch and duration. The key is modifying the wav file header sample rate directly. This changes the way the file contents are interpreted.
post edited by js516 - 2015/05/29 11:09:56
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Beepster
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Re: How do you old school playback tape audio at half speed?
2015/05/29 11:04:43
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js516
Slip streatch keeps the pitch constant while altering duration.
The easiest way to reproduce halfspeed/double speed playback is to record at half
/double the intended sample rate, then alter the header of the sample file to the intended sample rate.
In other words, if you're intended sample rate is 48k and you want to reproduce a halfspeed effect, record at 96khz then use a wav editor (audacity for example) to change sample rate value the header in the wav file to 48khz. When you playback the modified file, it will have twice the duration and half the pitch of the original.
Going the other way needs an extra step. Assuming the intended rate is 48khz, recording at 24khz is a bad idea. In that case i would record at 48khz, the modify the rate in the header to 96khz. This modified file will playback at double the pitch and half the duration. The additional step is to downsample the modified file to 48khz to maintain the altered pitch and duration.
The key is modifying the wav file header sample rate directly. This changes the way the file contents are interpreted.
I did not know it could be done that way. Cool!
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js516
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Re: How do you old school playback tape audio at half speed?
2015/05/29 11:14:31
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☄ Helpfulby mettelus 2015/05/29 11:57:03
http://www-mmsp.ece.mcgil...formats/wave/wave.htmlIf you're interested in wav file hacking, here's a good definition of the file spec. However, you're better off using a wav file tool to manipulate the sample rate (audacity can do this) instead of a hex editor. ;)
post edited by js516 - 2015/05/29 11:25:01
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ShellstaX
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Re: How do you old school playback tape audio at half speed?
2015/05/29 11:30:31
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I'm not familiar with slip-stretch etc ... but FYI ... I was playing with a free Beta VST recently that had a few tricks up it's sleeve. ToneCarver tcStretch for time stretching (ridiculous amounts), pitch shifting, and blurring. You might be able to do something with the routing on that,
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Beepster
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Re: How do you old school playback tape audio at half speed?
2015/05/29 11:55:32
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js516
http://www-mmsp.ece.mcgil...formats/wave/wave.html
If you're interested in wav file hacking, here's a good definition of the file spec. However, you're better off using a wav file tool to manipulate the sample rate (audacity can do this) instead of a hex editor. ;)
Thanks. I guess I really should learn exactly what a wav file is and how it is constructed considering I use and create the buggers all day. I kind of always left the bits and bytes mangling up to the computer/programs but I supposed if I want to really advance that's the type of crap one should know. lol... I just wanted to play my guitar. Now i'm turning into a nerd. It's a good thing. ;-)
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slartabartfast
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Re: How do you old school playback tape audio at half speed?
2015/05/29 16:35:32
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Changing the wave file header with an editor will indeed change the way the wave file is interpreted. But the playback will likely not give the result you want. Tape is a physical medium with more or less continuous analog modulation. As the speed of the tape over the head is altered, it will produce a more or less continuously variable change in pitch/duration. A wave file is a collection of samples of a continuous analog signal. It can represent an analog signal via the sampling theorem, but changing the rate at which the samples are played back, alters the relationship between the original signal and the digital model. Re-sampling is what is required if you do not want to lose fidelity, and there is more to re-sampling than just changing the sample rate in the wave header. When changes as large as 2X are contemplated, the use of filters may be necessary to avoid aliasing. A good varispeed algorithm is going to require more than just a sample rate change.
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Kalle Rantaaho
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Re: How do you old school playback tape audio at half speed?
2015/05/30 07:05:24
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^^^^ That's what I was thinking, too. Slowing down by 50% hardly takes place without artefacts of several kind knowing that the original medium is analog tape.
Speeding up might produce a better result. Well, I've never tried so maybe my pessimism is wrong.
As some others, I wonder, what was the reason to digitize the tapes at wrong speed.
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tlw
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Re: How do you old school playback tape audio at half speed?
2015/05/30 08:40:11
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Kalle RantaahoAs some others, I wonder, what was the reason to digitize the tapes at wrong speed. Lazy digitising without listening to the tapes? Only a single speed tape deck available? If the tapes are an assortment recorded at say 7.5ips, 15ips and 30ips but the person doing the digitising just ran them all through the tape deck at 15ips that would explain it. Whatever the reason it's a far from trivial job trying to sort that out.
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Anderton
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Re: How do you old school playback tape audio at half speed?
2015/05/30 10:45:18
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If the tape is recorded at half or double speed and the length changes as a result, you can use the Loop Construction window (but not to create a groove clip per se) to shift pitch and correct length at the same time.
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Re: How do you old school playback tape audio at half speed?
2015/05/30 12:21:46
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Thanks guys, I was really interested to read that I hadn't missed something simple. I think metelus and others have found the path to follow outside SONAR.
The issue is that some tape is 2 track, some 4 some mono, some stereo. Some is recorded at 15ips, some at 7, some 3.5 and - just possibly - half that. I don't have all the playback machines with all the speeds.
Also some of the tape is very old (1960s). Some of it is studio, some just mics left hanging out recording live at gigs, some it is demos. Often you only get one real shot at threading to find out what you have.
But I know that recording and playing back with a Roland RAP-10 card in the 90s worked just fine. That Roland card was bundled with ATW (Audio Tool Works): all you had to do was tell ATW to play at double the sample rate in an simple varispeed playback.
So I think that Audacity (which I've used) could work just the same. Great suggestion - I will report back shortly!
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TheSteven
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Re: How do you old school playback tape audio at half speed?
2015/05/30 13:17:06
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Some more info for you (edited out out of context info): (from http://forums.stevehoffman.tv/threads/software-for-changing-tape-speed.334356/#post-9641432 ) The only true tape equalization difference is between NAB (15 IPS) and CCIR (30 IPS),..
The equalization problem occurs here because you're either halving or doubling the NAB curve, moving it either up or down an octave. This was a real problem with some CBS half-speed mastered albums, when they didn't re-equalize the playback equipment to compensate. So when you double the 7.5 IPS tapes to 15 IPS, it's going to have too much top end and not enough bottom end. This picture is what the NAB curve looks like. ..
The easiest thing to do would be to just apply a filter with a bit of "tilt" to the new file, to slightly reduce the highs and boost the bass. It actually sounds a lot more complicated than it is, and the resulting file should be pretty decent. Attached Files:  NAB curve.jpgFile size:51.5 KB
post edited by TheSteven - 2015/05/30 13:26:53
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TheSteven
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Re: How do you old school playback tape audio at half speed?
2015/05/30 13:20:38
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Information on manually changing sample rate by editing wav file: If you don't have Audition or RX and Audition or whatever other software you have doesn't allow this kind of direct change of the sample rate stored in the file, it's possible to change the file using a freeware hex editor called Neo (http://www.hhdsoftware.com/free-hex-editor).This takes a bit more careful attention. The following site explains how wave files headers are structured: https://ccrma.stanford.edu/courses/422/projects/WaveFormat/Here's the example posted on that site with the four numbers represented sample rate larger and bolded:52 49 46 46 24 08 00 00 57 41 56 45 66 6d 74 20 10 00 00 00 01 00 02 0022 56 00 00 88 58 01 00 04 00 10 00 64 61 74 61 00 08 00 00 00 00 00 0024 17 1e f3 3c 13 3c 14 16 f9 18 f9 34 e7 23 a6 3c f2 24 f2 11 ce 1a 0dThose numbers represent in this case, a sample rate of 88,200 but as written in hexadecimal format. If you switch the Windows calculator to Scientific in the View menu, choose the Dec format button under the number display, enter 88200 then change to Hex format. You will get 15888. the way a wave file header stores this information is by groups of two digits reversed so 15888 becomes 88 58 01 00 (with zeros padding out to four groups of two digits).Here are the common sample rates plus any you'll use for doubling or halving22050: 22 56 00 0024000: C0 5D 00 0044100: 44 AC 00 0048000: 80 BB 00 0088200: 88 58 01 0096000: 00 77 01 00176400: 10 B1 02 00192000: 00 EE 02 00352800: 20 62 05 00352800: 20 62 05 00384000: 00 DC 05 00I know this might seem complicated but once you do it a couple of times, the procedure is really quite simple. The Neo hex editor I mentioned above is easy to use and provides the possibility of backing up the file you're working on in case you get it wrong. Practice a couple of times and you'll be fine and the results will be better sounding than speed changing software.As for freeware resampling that does a decent job, there are several, but one of the best is called SoX (http://sox.sourceforge.net/). Note that it's a command line (DOS) program, so it takes getting used to. You could also use the freeware program Foobar 2000 (http://www.foobar2000.org/) and then install an add-on to it for the SoX resampler (http://www.hydrogenaudio.org/forums/index.php?showtopic=67373). Source: http://forums.stevehoffma...d.334356/#post-9641978
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Beepster
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Re: How do you old school playback tape audio at half speed?
2015/05/30 13:28:21
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I am waaaay post tape/analog era audio nerd but it may be helpful to the older doods (I don't mean that as perjorative... perhaps more experienced with tape would be more appropriate) if you said what playback devices you do have available to you. They may be able to recommended ways to get the actual tape devices to play back at the proper (or at least as close to proper) speed.
The idea when transferring to digital like this is to get the best signal from the tape outputting from the analog gear into the computer. In this case of course ideally you want the tape to playback at the correct speed but if that is impossible then using the CLOSEST speed and capturing that would mean less digital manipulation after the fact (which would result in less potential digital artifacts). Also the REALLY experienced dudes may be able to give you some tricks to fiddle with the tape machines in some wizardly way to force them to playback at a more appropriate speed. Like "oh yeah... I know that machine. It has whatchamagigdget setting. Twist it to that then do this in the computer" or "If you yank off panel A you'll see Screw B and you can adjust playback speed".
But yeah... get the playback speed from the device as close as you can going into the box and it will result in better quality when you bend it in the digital environment. Personally if I had sessions that were really important I would go so far as to even rent the proper tape device(s) for the digitization process.
Cheers and cool topic.
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dilletant
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Re: How do you old school playback tape audio at half speed?
2015/05/30 18:14:41
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Try this:
insert a software synth capable of playing wav files (Drop Zone, Dimension, Rapture, SFZ player);
drag your file into the synth;
now you can vary the speed+pitch of the file by "playing" it on different keys. Let's say the original pitch is on C3, in that case C2 will play one octave lower.
Now insert long C2 note into midi track. The note suppose to be at least twice as long as the file, so it will play the file to the end.
Freeze the synth.
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fireberd
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Re: How do you old school playback tape audio at half speed?
2015/05/30 18:32:21
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Interesting. I don't have anything to suggest to try and resolve the problems. But, I come from the tape era and maintained a studio in Kansas City, Mo in the 70's (Big K Records) that had a 4 track Teac recorder and a 2 track Ampex.
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