Hi all

I've been putting some of my tapes onto hard drive and noticed that most of them are not "balanced"; either the left or right channel always seems a bit louder than the other....

Is this normal? A sign of a problem with the tapes? Or a sign of a problem with the player?

Apologies in advance if it is a daft question. I don't know a great deal about tapes.

Cheers

Max

If it is consistently biased towards one side then it is probably a head height error or a replay electronics misalignment.

H

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Technical Editor, Sound On Sound

No, not consistently one side.... It varies.

Thanks for the reply.

Most music varies moment to moment, obviously... You need to evaluate instruments that should be solidly in the centre -- lead vocals being the obvious example.

If stuff that really should be stable in the centre is moving around, then you're probably suffering from tape wave, where the tape guides or pinch roller/capstan are badly worn causing the tape to move randomly (or cyclically if it's a worn pinch roller/capstan) up and down across the head gaps.

H

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Technical Editor, Sound On Sound

Most DAW software can generate tones and noise, Audacity certainly can, mono and two channel.

Record a few minutes of 300Hz (1kHz is a "high" frequency for cassette!) at 10dB below Dolby and play and monitor the result. Do this for a variety of cassettes to prove whether it is tapes or the machine that is causing the trouble. TBH only really top bllx transports with "dual loop" capstans are really good in this regard.

Then put a 10sec clip thru Right Mark Analyser and be staggered at the distortion!

Dave.

Quote Li-rocchi:

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No, not consistently one side.... It varies.

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Music does that. Or it may have been recorded "off centre" for any number of reasons - intentional or otherwise. It doesn't sound as if your player is the culprit - that would affect EVERY track.

Stick one of the tracks into a wav editor and try a Normalise without channel linking. Does it sound better? Your choice.

Maybe this is like those bar-graph displays above the eq sliders on cheap domestic hi-fi. A surprising number of punters think their job is to adjust the sliders to equalise display levels of each band.

Edited by Hugh Robjohns (22/02/13 03:38 PM)

I often find that modern computer meters magnify the imperfections that older metering and LED bargraphs didn't pick up. If we're talking about a difference of 2dB or less then it could well be down to metering limitations when the tapes were recorded.

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

Some people certainly do place far too much importance on the metering, and far too little on their ears! The idea of the meters is to confirm what your ears are telling you, and to provide an absolute static level reference for the recorded signal.

As I was explaining above, if something that is obviously supposed to be central isn't -- and especially if it is clearly wandering about the image -- then there's a problem. But if the centreal sources sound central adn stable, I wouldn't worry about the meters fighting over which one is loudest.

But if you really don't trust your ears and/or monitoring, then a goniometer of lissajous display provides a fabulous sanity check for imbalance issues.

Hugh

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Technical Editor, Sound On Sound

Oh dear. More memories

Who was the numpty that had the bright of making tape guides with a nice hard chrome finish... on top of butter-soft brass?

And then there was the fight we had with Akai over their glass-ferrite head lifetime guarantee. They tried to claim that our customer's use of Cr02 tapes was 'abnormal' wear.

Oh how we laughed.

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It wasn't me!
(Well, actually, it probably was)

Quote Folderol:

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Oh dear. More memories

Who was the numpty that had the bright of making tape guides with a nice hard chrome finish... on top of butter-soft brass?

And then there was the fight we had with Akai over their glass-ferrite head lifetime guarantee. They tried to claim that our customer's use of Cr02 tapes was 'abnormal' wear.

Oh how we laughed.

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Well the guides have to be non-magnetic Will so that really only leaves certain stainless steels and ceramics both of which are expensive to manufacture.

Re tapes and headware: There was a story that Scotch video tape was very abrasive but I don't think anything was ever proved?

Dave.

Hi all

A quick follow up on this....

I managed to rig up a second tape player and that player exhibited the same issue as the Technics deck.

I then tried out some different leads, different inputs on the sound card, etc. Did not make a difference. Shortly after that I realised I was being stupid; it was obvious that there was no fault with the leads or connections anywhere because the VU meters on both decks were showing the L/R differences.

As I've checked more and more tapes, it seems that the vast majority of them have a boost on the left channel, usually between 2 and 3 dB but sometimes less. The rare tape shows a boost on the Right channel (usually less in terms of dB). And there was one tape that kept switching from track to track.... It was a techno set, and each time the next record was mixed in, the "bias" would change.

Just to clarify, the bias is a very obvious one visually. The peak meters on my software and on the decks peak consistently higher on the louder channel. The RMS meter shows the difference, and the RMS average figure makes it obvious. Finally, the phase meter is has a permanent slight slant, showing 2 minutes to 6 on the majority of tapes.


So I guess I'm none the wiser. If anything, I'm a bit more confused now! I thought I'd share though in case any of this is helpful to those more knowledgeable in such matters than I am!!!

All the best

Max

Quote Li-rocchi:

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I managed to rig up a second tape player and that player exhibited the same issue as the Technics deck.

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If the source tapes were recorded on a misaligned machine, this is what you'd expect.

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As I've checked more and more tapes, it seems that the vast majority of them have a boost on the left channel

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Where have these tapes come from? Are they commercial tapes, or home made? Both were prone to being badly aligned.

Quote:

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there was one tape that kept switching from track to track.... It was a techno set, and each time the next record was mixed in, the "bias" would change.

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That could only happen at source and clearly involved misaligned recording feeds fromthe two sources.

Quote:

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Just to clarify, the bias is a very obvious one visually. The peak meters on my software and on the decks peak consistently higher on the louder channel. The RMS meter shows the difference, and the RMS average figure makes it obvious. Finally, the phase meter is has a permanent slight slant, showing 2 minutes to 6 on the majority of tapes.

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Peak meters can be very misleading in these cases, as I explained in this thread long ago. RMS meters are usually a better indication becuase of the longer-term averaging. Phase meters don't have a 'slant' they simply give a reading between -1 and +1... so I think you're talking about a Goniometer of Lissajous display. As I said way back... this is the best way of assessing whether there is a level ofset or not becuase sounds that should be central -- bass drum, vocals, etc -- should manifest as a vertical line, or a vertical mains axis in the display 'blob'. If it is slanted over then you have a level offset, and all you need to do is tweak the balance of the replay channel (or trim one side's input gain or fader) to realign the vertical axis. Simples

H

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Technical Editor, Sound On Sound

- The source tapes were recorded on a variety of machines, by a number of quite a few different people in lots of different places....

- The majority are homemade. I've got only a couple of originals left now.

- Yep, on your advise I've been focusing on the RMS readings. I just mentioned the peak meters because they are present on the tape decks themselves. And whilst they may not be the best indicator, I thought that their behaviour may still be relevant. On a typical tape, the needle on the L channel would mainly bounce and live between -3 and 0. Whereas on the R channel, although it would be bouncing to the same time and movements of the L, it did so between 0 and +3.

- They call it a Phase Meter in Wavelab (that's where I got the term from and the info RE "slanting"). I'm not saying they're right......

- Thanks for the info re how to correct it. I do like a "simples" solution! And it does sound like an easy fix. I guess I've just got the curiosity bit between my teeth and would love to get to the bottom of why the tapes mostly all have the same bias. Could it be anything to do with how the tapes have been stored?


Many thanks (as ever) for the great help.

Max

Quote Hugh Robjohns:

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there was one tape that kept switching from track to track.... It was a techno set, and each time the next record was mixed in, the "bias" would change.

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That could only happen at source and clearly involved misaligned recording feeds from the two sources.

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The channel matching on cheap magnetic cartridges is often specified to be within 2dB which could easily account for this sort of thing - although, if the DJ mixer had trim controls on the inputs, it could also be down to errors in setting the trim control. It is actually fairly hard to set the channel balance accurately with a stereo music signal. You really need a known mono source in good condition.

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

Quote Li-rocchi:

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I guess I've just got the curiosity bit between my teeth and would love to get to the bottom of why the tapes mostly all have the same bias. Could it be anything to do with how the tapes have been stored?

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I wouldn't have thought so. The left channel stripes on compact cassette are on the outer edges, with the right channels towards the centre. Edge damage through poor tape packing inside the cassette shell would tend to damage the left channel more than the right -- but you're experiencing the reverse of that.

The most likely reasons are poor electrical alignment of the casette machine's internal electronics, either during recording or replay, or both -- or poor recording level setup by the tape originator or poor balance from the source.

Few if anyone would notice small level balance misalignments from the waggling VU meters on most cassette machines or mixers, and probably fewer would care...

As I said, I wouldn't worry about it, just tweak the balance to correct it in your DAw and move on...

Hugh

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Technical Editor, Sound On Sound

Quote Li-rocchi:

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As I've checked more and more tapes, it seems that the vast majority of them have a boost on the left channel, usually between 2 and 3 dB but sometimes less.

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Were these tapes all recorded on the same machine?

Quote Exalted Wombat:

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Were these tapes all recorded on the same machine?

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two posts below the one you quoted:

Quote Li-rocchi:

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- The source tapes were recorded on a variety of machines, by a number of quite a few different people in lots of different places....

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Technical Editor, Sound On Sound