Bruce B
WBF Founding Member, Pro Audio Production Member
And tapes that were recorded on units that exhibit bumps at different frequencies and amplitudes, you do what? Of course you only play at 15ips, correct?
United Home Audio Phase 11S deck has been ordered
- Thread starter rockitman
- Start date
And tapes that were recorded on units that exhibit bumps at different frequencies and amplitudes, you do what? Of course you only play at 15ips, correct?
And tapes that were recorded on units that exhibit bumps at different frequencies and amplitudes, you do what? Of course you only play at 15ips, correct?
So how would the UHA deck be any better in this regard? I thought that was what Christian was talking about. That goes back to the post by JZDA that the best sounding machine is one that's properly aligned.
As far as speed, yes only 15ips.
Bruce B
WBF Founding Member, Pro Audio Production Member
You need to answer my question Myles as it was directed to you, not to or about Christian's machine.
How is this "resistor" going to correct for head bump at different frequencies and amplitudes from tapes that were recorded on a hundred different machines?
Gentlemen
I do believe you are arguing about different diseases here:
"Head Bump" is a playback only phenomenon that occcurs by interaction between the physical properties of the Playback head and the recorded signal.It is not a recording phenomenon.
The troublesome overbearing bass experienced by those using outboard repro amps may well be due to this.It is also a reason to argue against the use of universal repro amps as the bump is specific for each type of head. Hence the resistor fix for Myles' Nortronics heads(remember the Cello electronics were exclusively design for the Studer A 820) will be a disaster for X or Ys Woelke or FM or whatever.
According to Jay McKnight there are three reasons for bumps in playback;(1) Headbump, we dealt with (2) Tape Fringing ,which is really only a calibration tape phenomenon and (3) indifferent equalisation during recording which is likely to be the one that has Bruce tearing his hair out. We only have to look at the weird way in which the NAB curve addresses low frequencies to realise the difficulty in putting Humpty Dumpty together again 30-40 years after the fact.
Of concern is also how aftermarket switchable eq repro amps deal with the low freq differences between NAB and IEC curves : IEC has no eq at LF while NAB has a 20db boost starting at 50Hz carrying on downwards ad infinitum. In effect freqs below 250Hz are already boosted. Some manufacturers ignore the effects at LF and only switch for the HF causing overbearing bass on IEC tapes
Then at High Frequencies there are such delights as head gap compensation,cable capacitance compensation etc that makes one want to leave a stock machine... well stock.
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As most of my tapes are IEC, that is what I am experiencing with them. Bass that is a bit overbearing.
Bruce B
WBF Founding Member, Pro Audio Production Member
That's right... and the recorded signal is different depending on what playback head you use to calibrate/monitor. That's why test tones are on tapes (hopefully) so you can do LF calibration depending on what machine it was recorded on and how it was set up.
Jack Endino posted how 10 machines can have 10 different freq/amplitude headbumps. Now you have to compensate for that somehow when duping from tapes recorded on 10 different machines! Otherwise, you would not need test tones on tapes... just set every machine with an MRL tape.
And that is the difference between you and the rest of us. For me it only has to sound good to my ears.My gut wrenching bass may well be Rockitman's overbearing or vice versa. You have to make it correct. And what is that?
On the production master there will hopefully be a 100Hz tone to eq bass and another at 50Hz to compensate for the head hump. That tone will be recorded on to the machine that made the master? What about the bumps on the playback of the Multitrack machine(the ones Endino measured) and the playback of the mixdown etc. PF's The WALL was recorded in the south of France,bits in England, flown to the US, mixed down there,flown somewhere else,mastered there, flown somewhere else to have production masters made ,cut and bought by me as an audio masterpiece.How many different machines with how many different settings in there. What on earth did I buy?
Pros must really hate Audiophiles. Every time I hear Rumours I wonder why they can't just lift the trebles a bit and cut the upper bass/low mids a little to make it sound more lively and open. Do that and for everyone who likes that there will be 3 others who run to their album racks,pull out a NM first pressing and cry foul! Down with the concept of the Absolute Sound and bring back tone controls!
Didn't Mark use his module with the A80 too eg. the ML5?
As far as modding question goes. I think that people like Charlie and Nick go and check the decks FR. IIRC, Charlie also uses a HF trim in his unit.
On all of them? If I'm reading Bruce correctly, this phenomena should vary from tape to tape.
It will ensure that your machine is not contributing to the issue. It's not dissimilar from arguing about room Rx.
I'm not with you re the module and ML 5? Is it the similarity between the ML5 and Cello? The ML 5 was designed as a unit with the A80 RC ,right down to the specified butterfly only heads.It used the Mark Levinson modules as used in the then pre amps.Tom Colangelo designed both but I'm not sure how the ML5 relates to the later Cello unit. My guess would be not at all? Charlie King should know as he owns both ML5 and P603 modules. The ML5 runs off a +/- 15V regulated supply and is a single ended design while the Cello P603 runs off +/- 30V and is balanced out. I'm not sure if the P603 is inherently single ended with conversion to balanced in the output module P301.
Re the Cello being A820 specific. My fault-this from the Cello literature:
The Cello Audio Suite Mainframe can
be equipped with P603/P301 modules which serve as state-of-the-art playback electronics
for decks by Studer, Telefunken, Ampex, and other companies.
I'm not sure how they dealt with the different heads.One thing is sure : A Fully laden Audio Suite P603/P301 is a fine looking animal (Courtesy Fred Thal):
A billion apologies to Rockitman for totally derailing his thread. Consider it punishment for abandoning an A80 for a Teac, of all things!:b
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No apology needed. I learned something here. Cheers !
actually a Tascam shell that provides a frame, spooling motors and front panel controls. Anything to do with sound repro is not Tascam.
Yes, Christian's excess bass problem is likely due to un-corrected playback head "bumps", but sometimes it can have nothing to do with that. Some RTRs I've tested that have switchable EQ (NAB/IEC), only switch the HF EQ. They leave the bass EQ always in the NAB position. (NAB bass EQ is a 3db boost @ 50Hz in record and a 3 db cut @ 50Hz in play).
If you were to record on one of those decks set to IEC EQ (with an improper NAB record bass boost) and then play back on another deck with standard IEC EQ (which has flat bass response), then the resulting tape would be bass heavy. 50Hz would be boosted 3 db.
As has been mentioned in this thread, bass response can definitely be altered from flat by the play head. However, almost any decent quality deck you record on will have flat bass response. I'm referring here strictly to the signal recorded on the tape. The recorded bass signal will be quite flat (assuming IEC EQ) and not have any "bumps". Reason is that it's easy to design a record amp with flat bass response (flat down to 20 or 30 Hz) and also because a decent-quality record head does not significantly effect bass response. So, in theory, if one were to listen to many first generation tapes made on many different machines, the bass should be quite flat in all of them. However, the majority of "master tapes" are 2nd or 3rd generation, so yes, the random effects playback head bumps do come into play.
Play head "bumps" are caused by the shape of the head surface and other head-design factors. Some heads have small bumps and those should be ignored. Some heads can have a 5-6 db bass bump, however. Heads like that should be corrected by introducing a low-end electrical response cut to the play amp. This type of compensation should only be done as a last resort because the bass quality (phase response) can sometimes be degraded as a result.
To measure low-end play response and see if you have unacceptable head bumps, you can't play a standard test tape. First you need to verify that your play amp's bass response is, in-fact, flat (for IEC) or has a -3 db cut at 50 Hz (for NAB). This is done by injecting test-tones into the play head via a "loop generator". Then you need to verify that your record amp is, in fact, flat (for IEC) or has a +3 db boost @ 50Hz (for NAB). You do this by connecting a 100 ohm resistor in series with the record head ground lead. Then turn off the bias oscillator and measure the audio voltage drop across the resistor. Check tones 20Hz to 1KHz. If correct, then record and play back the same low frequency tones (20Hz to 1KHz). Any deviations from flat bass will be the result of "head bumps". If only, say, 2 db boost at 30 Hz, then do nothing. If a lot more, then consider rolling off the low-end of the play amp electronics. This is usually done by changing a resistor value in the play amp EQ stage feedback loop. This is the resistor change that Myles was referring to.
So at least for first-generation tapes, low-end "head bumps" don't vary tape to tape. They will for multiple generation tapes, of course, since playback heads are involved with those. Differences in bass response we hear can be a play head to play head variation. Or a play amp that has been compensated for head bumps vs. a head amp that has not been compensated for head bumps. BTW, decks fitted with very high quality play heads typically don't have or need any bass compensation/correction in the play amp. That's the best way to go sound-wise.
If you were to record on one of those decks set to IEC EQ (with an improper NAB record bass boost) and then play back on another deck with standard IEC EQ (which has flat bass response), then the resulting tape would be bass heavy. 50Hz would be boosted 3 db.
As has been mentioned in this thread, bass response can definitely be altered from flat by the play head. However, almost any decent quality deck you record on will have flat bass response. I'm referring here strictly to the signal recorded on the tape. The recorded bass signal will be quite flat (assuming IEC EQ) and not have any "bumps". Reason is that it's easy to design a record amp with flat bass response (flat down to 20 or 30 Hz) and also because a decent-quality record head does not significantly effect bass response. So, in theory, if one were to listen to many first generation tapes made on many different machines, the bass should be quite flat in all of them. However, the majority of "master tapes" are 2nd or 3rd generation, so yes, the random effects playback head bumps do come into play.
Play head "bumps" are caused by the shape of the head surface and other head-design factors. Some heads have small bumps and those should be ignored. Some heads can have a 5-6 db bass bump, however. Heads like that should be corrected by introducing a low-end electrical response cut to the play amp. This type of compensation should only be done as a last resort because the bass quality (phase response) can sometimes be degraded as a result.
To measure low-end play response and see if you have unacceptable head bumps, you can't play a standard test tape. First you need to verify that your play amp's bass response is, in-fact, flat (for IEC) or has a -3 db cut at 50 Hz (for NAB). This is done by injecting test-tones into the play head via a "loop generator". Then you need to verify that your record amp is, in fact, flat (for IEC) or has a +3 db boost @ 50Hz (for NAB). You do this by connecting a 100 ohm resistor in series with the record head ground lead. Then turn off the bias oscillator and measure the audio voltage drop across the resistor. Check tones 20Hz to 1KHz. If correct, then record and play back the same low frequency tones (20Hz to 1KHz). Any deviations from flat bass will be the result of "head bumps". If only, say, 2 db boost at 30 Hz, then do nothing. If a lot more, then consider rolling off the low-end of the play amp electronics. This is usually done by changing a resistor value in the play amp EQ stage feedback loop. This is the resistor change that Myles was referring to.
So at least for first-generation tapes, low-end "head bumps" don't vary tape to tape. They will for multiple generation tapes, of course, since playback heads are involved with those. Differences in bass response we hear can be a play head to play head variation. Or a play amp that has been compensated for head bumps vs. a head amp that has not been compensated for head bumps. BTW, decks fitted with very high quality play heads typically don't have or need any bass compensation/correction in the play amp. That's the best way to go sound-wise.
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Yes. But then of course you also have to talk about matching heads to the electronics.
Their standard line of replacement heads were never considered "very high quality" or "state of the art" at all. However, I have heard reports that they did make a line of higher-end "professional" heads. I have no experience with those. Certainly possible they work and sound fine (or, with some adjustments to the playback amp, work and sound fine).
AFAIK their "professional" and "semi-professional" heads are the only ones currently sold?
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