fluxivity and MOL as a function of tape speed?

sweetbeats

sweetbeats

Reel deep thoughts...
So let me get this right...my mind was wanering as it often does, and I started thinking about the benefits ans detriments of 30ips vs. 15ips...am I correct in that if you hit the tape with saturation-level at 15ips, would you then be below saturation level if you switched to 30ips because there would be more oxide to absorb the same level of flux at 30ips compared to 15ips?
 
I believe so, yes!

You also decrease audible tape hiss another 10 db, (on average), double the high frequency response and lose the bottom octave of your bass response if the heads were only designed for 15 ips. You'll also wear the heads down twice as fast along with the guide-posts...but I'm sure you knew all that already! ;)

Cheers! :)
 
Yeah...i did know about all the other stuff, just never really concretely landed on the whole headroom thing.

Jumping to 30ips can do ugly things to your response curve if the heads weren't designed for it.

I'm just poking around at the idea since I may be getting access to a DC capstan motor for my MM-1000 which will open the possibility of 30ips and its good (in my mind anyway) to ponder the reasons and potential in trying it out...what to test, what to listen for, that sort of thing.

The repro head is pretty wide, though not wide enough as far as I can tell to do a good job capturing those subsonic tones at 30ips...It'll be interesting to mess around with it at some point though and who knows? I may be surprised.
 
The other thing you might want to look at is how clean or not so clean the channel amp units of the MM1000 are. I remember looking at some s/n ratio specs on the 440 series and noting that the signal to noise specs were a bit on the low side compared to mid line TASCAM recorders like the 48 which were achieving 68 to 70 db s/n ratio specs without noise reduction while the 440 specs were at least 3 db worse, which is audible and cumulative, the more tracks you have.

So the point of all this is to be concerned that even if you went up to 30 ips, your electronics might still be adding audible hash to the sound.

Cheers! :)
 
I hear you...

Thing is, I don't think the spec sheets are apples-to-apples between, say the 48 and the MM-1000/440. I had a 440B electronics module on the bench to test it, and granted my test only took the input amp into account as I was only monitoring the input through the module, but I had it connected to my beat-up M-308B and I was using an SM-57 and monitoring via headphones...I thought I had the mic channel open to the electronics module but I didn't. I was monitoring the return. I had the input and output knobs cranked up on the electronics module because I wasn't getting anything from the mic but the problem was that I forgot to turn the GROUP channel ON on the mixer. Anyway, there wasn't any noise to speak of at all and that shcoked me because I expected there would be a ton with an untouched original 40 year old 440 module but nope...and then like a dummy I realized the GROUP channel wasn't on and when I switched it on the road noise from the road a couple hundred yards away was deafening in the cans and I was in the enclosed shop. So I'll keep that in mind but who knows what'll happen with this system at 30ips...the electronics are rated to handle like +28dBu before clipping and with tape streaming by those wide-format heads at 30ips using 499...we'll see.
 
Another advantage of faster tape speed is more precise editing. Punch ins and outs are tighter.

I think it's unliikely the record amp will be noisier than the tape noise itself. Any good transistorised electronics from the late 60's onwards was pretty quiet compared to the analog tape noise. This is the perhaps uncomfortable truth, not about analog per se but about analog recording methods.

How could it be that the record elecronics from a 40 year old tape machine can have better noise/distortion/dynamic range performance than the latest and best analog tape stock from 2009? Both are analog systems but the analog recording system cannot match the analog record amp that is driving it.
BTW at 30 ips with modern tape the potential high frequency limit is probably in the hundreds of kilocycles, although in practice bcause of head limitations it will be much lower than that. But it also demonstrates just how wasteful of data bits is the analog audio tape system when using high tape speeds.

15ips and 30ips were used partly for better editing and partly to reduce tape noise but there's a law of diminishing returns here.

Maybe food for thought.
 
My only open reel decks are in the Tascam 22 family (a couple of 2-tracks and a 4-track), which were all made for tapes like Ampex 407 (+3).

I can say that using a tape like Scotch 207 (also +3) sounds great at 15 IPS. Switching to 7.5 sounds bad. On the other hand, LPR35 (+6) sounds better to me at 7.5 than 15. Like at 15 IPS, the Tascam electronics distort before there is any saturation. 7.5 IPS on the LPR35 seems right.

Just my subjective observation, but it supports what you are saying.
 
Tim, thanks...yeah I was thinking that it is a truncated thought to exclude the rest of the system when considering noise (i.e. looking only at the amp electronics)...the thing I'm finding with the Ampex stuff I have in the 440 and MM-1000 family is that the PSU's produced really clean power and I have to theorize that that can't but help with noise in the audio circuits downstream. I'm just really excited about these old electronics units.

I have a feeling that when up and running I will mostly or entirely focus on utilizing 15ips...cheaper and I'm anticipating that I'll miss the LF bump at 30ips...all just silly daydreamy stuff right now though which is pretty much all the good this thread is! :D
 
I think 30 ips really has more of a rightful place in stereo mastering where you want to "bark up", to borrow a military term. And following that logic, if you were multi-tracking at 30, then you should most certainly want to master at 60! :p:D:D

Cheers! :)
 
The Ghost of FM said:
I believe so, yes!

You also decrease audible tape hiss another 10 db, (on average), double the high frequency response and lose the bottom octave of your bass response if the heads were only designed for 15 ips.
Click to expand...

FYI, the spec sheet for RMG SM 468 shows a 2.0 dB difference in dynamic range at 30 ips vs 15 ips via both IEC and CCIR bias noise measurement standards. For SM 911, they show 3.5 to 4.0 dB difference in dynamic range. I've never noticed a difference bigger than that.

Also, in the real world, frequency response will probably not actually double, since the 15 ips response could easily be pretty good out to 25K (like my little Otari 8-track) and the overall system (tape and electronics) may still start to roll off at 30K at 30 ips (and most all your mikes start to roll off big time by 20K if not below). Mikes that don't roll off until much higher tend to be noisy, because they have to be so small and the self-noise becomes a problem relative to the signal produced by the capsule.

As you say, you do typically lose about an octave off the bottom, though newer Studers and the Ampex ATRs are generally able to keep even the 30 ips response flat down into the 20 to 30 Hz region.

Cheers,

Otto
 
ofajen said:
FYI, the spec sheet for RMG SM 468 shows a 2.0 dB difference in dynamic range at 30 ips vs 15 ips via both IEC and CCIR bias noise measurement standards. For SM 911, they show 3.5 to 4.0 dB difference in dynamic range. I've never noticed a difference bigger than that.

Also, in the real world, frequency response will probably not actually double, since the 15 ips response could easily be pretty good out to 25K (like my little Otari 8-track) and the overall system (tape and electronics) may still start to roll off at 30K at 30 ips (and most all your mikes start to roll off big time by 20K if not below). Mikes that don't roll off until much higher tend to be noisy, because they have to be so small and the self-noise becomes a problem relative to the signal produced by the capsule.

As you say, you do typically lose about an octave off the bottom, though newer Studers and the Ampex ATRs are generally able to keep even the 30 ips response flat down into the 20 to 30 Hz region.

Cheers,

Otto
Click to expand...

So it sort of sounds like you're saying that his MM1000 is already more then good enough at 15 ips and perhaps not really worth it to get it to run at 30?

Cheers! :)
 
The Ghost of FM said:
So it sort of sounds like you're saying that his MM1000 is already more then good enough at 15 ips and perhaps not really worth it to get it to run at 30?

Cheers! :)
Click to expand...

Well, I guess if it were me, I'd get it going at 15 ips and see if I could get it to meet factory spec and see how I liked it and see if I felt any need to go to the trouble and expense of setting up for 30 ips. I don't recall how these machines are set up regarding tape speed, but if they are like the earlier AG series, they are two speed machines with AC sync capstan motors, so if it is 15/7.5, there will need to be a new capstan motor and new (or modded) record and play eq cards.

I kinda went through this thing this summer. I already had parts to convert my M-23 2-track from 15/7.5 rim drive to 30/15 belt drive, but it sounded good once I got it going at 15 ips. Plus I would have to mod the eq cards. I decided 15 ips was enough for me.

OTOH, I used to have a big console M-79 2-track that ran 30/15 and it sounded stellar at 30 ips... though I still generally ended up mixing at 15 ips.

Cheers,

Otto
 
The deal here is that I may have access to a DC servo capstan and the associated electronics for a very reasonable price and of course I'll want to give it a try at some point. Yes the AC hysteresis motor does 7.5 and 15ips, and the DC motor servo electronics can be strapped 3.75/7.5, 7.5/15, or 15/30. Can't like I said I imagine 15ips is going to be the ticket for how I like to track but its just one of those dumb 'this one goes up to 11' for me...I may run the AC motor and keep the DC motor on the shelf...who knows, but my mind was wandering through the pros and cons...the possibilities and that's where this thread came from. The DC motor brings the transport up to speed quicker, is more stable in its speed and (contrary to some DC servo systems when compared to AC motors) has a lower flutter spec.

I have plenty of spare EQ boards and it would be a relatively easy project to mod a set for the AES curve...a bit more of a challenge for me to mod a set to be switcheable between the 30ips AES curve and 15ips NAB or IEC...or all three...but if I end up having an affinity for a couple of those options then I may look into that. Anyway, its certainly off in the future. For the time being and maybe for always the MM-1000 is going to run at 15ips NAB with the AC capstan motor. ;)
 
sweetbeats said:
...am I correct in that if you hit the tape with saturation-level at 15ips, would you then be below saturation level if you switched to 30ips because there would be more oxide to absorb the same level of flux at 30ips compared to 15ips?
Click to expand...


Yes, you are correct. :)
 
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