Strange reel-to-reel record/playback speed problem..

matt_tricks · 1st August 2005

Calling all veteran engineers!

I've got an Akai GX-4000D 1/4" reel-to-reel machine I picked up from Ebay. It's a great unit with nice clean sound and in fantastic condition.. BUT..

I have a very strange problem whereby the playback speed seems to be fractionally faster than the record speed! The symptom is basically that when I bounce a track from my DAW down to tape and then back into the DAW, the track that I record back into the DAW is a little shorter (and therefore I'd assume higher pitch, although the difference is small enough to be inaudible). That means of course that it falls out of time with the rest of the track. The same goes if I record straight to tape and then "import" it into the DAW.

Has anyone ever experienced such a thing? I've checked the tape path and there's no extra heads in contact with the tape during recording or anything. I would assume that it would have to be exactly the same servo driving the reels for playback and recording so it's all a bit of a mystery to me. I'm not scared of wielding a screw driver and hammer on the thing if required but just thought I'd check here first. I'm a little bamboozled as to what could cause it but I don't have any previous experience with tape machines.

Thanks all.
Matt

themaidsroom · 1st August 2005

does it have a vari-speed knob that could be out of the notched space?

good luck

- jack

matt_tricks · 1st August 2005

Hi Jack,

Don't know what "notched space" is but the way I select tape speed is by screwing a special "capstan" on next to the rubber roller. When the capstan is in place the tape speed is 7ips, when off it's 3.5ips. I always have it on but it is on for both playback and recording so it should always run at the same speed?

I'm not sure exactly how it works because I'd imagine that the reels themselves would have to change speed but perhaps it regulates that somehow. At any rate, it seems to be inconsistant between playback and recording!

Matt

themaidsroom · 1st August 2005

all i could say is try it at the slower speed - you might learn something -
it doesn't sound like a great means of changing the speed of a motor, but
maybe i'm not visualizing it..............
are there any calibration knobs or screws that change the speed other
than the one you are talking about?

- jack

brianroth · 1st August 2005

That is a bit odd! The only thing that comes to mind is the power supplies are more heavily "loaded" during record mode, but that seems pretty bizarre in terms of shifting the speeds.

To verify the speed change, use a "steady" 1kHz (or whatever's convenient) test tone and cut it to tape. Immediately replay the tape while also listening to the tone from the generator to ensure the machine IS indeed playing back at a slower speed.

Bri

matt_tricks · 3rd August 2005

Thanks for all the info guys!! Between this and Recording.Org forums I've managed to determine that this is pretty normal from a consumer/pro-sumer device. I guess the voltage thing might not be as crazy as it sounds after all! Perhaps the thing is slightly underpowered. Who knows.

I ruled out random "drift" initially because it's ALWAYS faster on playback than record.

I guess the way I can use it now is with some sort of pitch shift but then I lose quality because of the algorithms involved so no go really.

Guess I'll start saving for the "real thing" and just use it as and where I can for bouncing down entire cuts that don't mind an extra couple of cents higher pitch!

Thanks again guys,
Matt

KarlHoffmann · 3rd August 2005

Matt,

Assuming that this is a three-head machine and assuming that you are trying to use it to get that "analog sound...warm, fat, tape sound....whatever.." , why not just record the repro output to the DAW while you're recording. You will have to slip the DAW track forward but that's simple to figure out. Record a click multed direct to the DAW and passing through the Akai while it's recording. Look at the two wave forms and you'll see the amount of record head to playback head delay. Of course, if the Akai is only a 2 head machine, this isn't going to work.

Karl

gyraf · 3rd August 2005

On most tape machines, you can't just dump the signal through record/repro in one take, as there's a lot of crosstalk from rec to repro heads. Generally they sound MUCH better when you rewind the tape and listen playback-only!

For your speed problem, that is completely normal - there is some 0.1% speed deviation even on very good machines. This is what timecode is ment to compensate for: stripe one track with a reference timecode, use something like a timeline lynx to sync to that, and you're flying.. But you'll need a tape machine with external varispeed and function control to run it as a slave from DAW..

Jakob E.

1st August 2005	#1
matt_tricks Gear nut Joined: Jul 2005 Location: Perth, Western Australia Posts: 127 Thread Starter	Strange reel-to-reel record/playback speed problem.. Calling all veteran engineers! I've got an Akai GX-4000D 1/4" reel-to-reel machine I picked up from Ebay. It's a great unit with nice clean sound and in fantastic condition.. BUT.. I have a very strange problem whereby the playback speed seems to be fractionally faster than the record speed! The symptom is basically that when I bounce a track from my DAW down to tape and then back into the DAW, the track that I record back into the DAW is a little shorter (and therefore I'd assume higher pitch, although the difference is small enough to be inaudible). That means of course that it falls out of time with the rest of the track. The same goes if I record straight to tape and then "import" it into the DAW. Has anyone ever experienced such a thing? I've checked the tape path and there's no extra heads in contact with the tape during recording or anything. I would assume that it would have to be exactly the same servo driving the reels for playback and recording so it's all a bit of a mystery to me. I'm not scared of wielding a screw driver and hammer on the thing if required but just thought I'd check here first. I'm a little bamboozled as to what could cause it but I don't have any previous experience with tape machines. Thanks all. Matt

1st August 2005	#5
brianroth Lives for gear Joined: May 2005 Location: Oklahoma City Posts: 1,818	That is a bit odd! The only thing that comes to mind is the power supplies are more heavily "loaded" during record mode, but that seems pretty bizarre in terms of shifting the speeds. To verify the speed change, use a "steady" 1kHz (or whatever's convenient) test tone and cut it to tape. Immediately replay the tape while also listening to the tone from the generator to ensure the machine IS indeed playing back at a slower speed. Bri __________________ Brian Roth Technical Services Oklahoma City, OK www.BrianRoth.com

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1st August 2005	#2
themaidsroom Lives for gear Joined: Apr 2005 Location: nyc / london Posts: 3,510	does it have a vari-speed knob that could be out of the notched space? good luck - jack

3rd August 2005	#6
matt_tricks Gear nut Joined: Jul 2005 Location: Perth, Western Australia Posts: 127 Thread Starter	Thanks for all the info guys!! Between this and Recording.Org forums I've managed to determine that this is pretty normal from a consumer/pro-sumer device. I guess the voltage thing might not be as crazy as it sounds after all! Perhaps the thing is slightly underpowered. Who knows. I ruled out random "drift" initially because it's ALWAYS faster on playback than record. I guess the way I can use it now is with some sort of pitch shift but then I lose quality because of the algorithms involved so no go really. Guess I'll start saving for the "real thing" and just use it as and where I can for bouncing down entire cuts that don't mind an extra couple of cents higher pitch! Thanks again guys, Matt

3rd August 2005	#7
KarlHoffmann Gear maniac Joined: Sep 2002 Location: Nerja - Spain Posts: 161	Matt, Assuming that this is a three-head machine and assuming that you are trying to use it to get that "analog sound...warm, fat, tape sound....whatever.." , why not just record the repro output to the DAW while you're recording. You will have to slip the DAW track forward but that's simple to figure out. Record a click multed direct to the DAW and passing through the Akai while it's recording. Look at the two wave forms and you'll see the amount of record head to playback head delay. Of course, if the Akai is only a 2 head machine, this isn't going to work. Karl

3rd August 2005	#8
gyraf Lives for gear Joined: Jun 2002 Location: Denmark Posts: 667	On most tape machines, you can't just dump the signal through record/repro in one take, as there's a lot of crosstalk from rec to repro heads. Generally they sound MUCH better when you rewind the tape and listen playback-only! For your speed problem, that is completely normal - there is some 0.1% speed deviation even on very good machines. This is what timecode is ment to compensate for: stripe one track with a reference timecode, use something like a timeline lynx to sync to that, and you're flying.. But you'll need a tape machine with external varispeed and function control to run it as a slave from DAW.. Jakob E.