Helicopter sound

[TONYFRANCE]

Hi,

I transferred a commercial tape.
Sound is like an helicopter behind the people voices.

My material is new.
The picture from the transfer is perfect. But the sound is strange.

There's no blinking light in front of my ADVC110, so I don't think it's a macrovision problem.
What is it ? And how can I remove it ? It's easy ? I know how to use Audacity to remove vinyl records pop/click. But this kind of artefact, is all new for me.

VHS Sound

[jagabo]

Adjust the tracking on the VHS deck.

[TONYFRANCE]

Thanks
It's rare ? Cause I thought automatic tracking was kind of perfect.

It happen often ?

Oh and there's nothing on screen, normal ? I'm blind when I adjust it.

[davexnet]

It is not perfect, probably works best if the tape was recorded on the same machine but even then
it may not be 100%., depending on tape condition.

Why don't you upload your samples to this site directly using the upload files/attachments button?

[TONYFRANCE]

Yes you're right. I will change the link.
Wetransfer is good but links are not forever. If someone find this topic in 2032, he will not understand the problem

[johnmeyer]

You might try transferring using a different deck, if that is possible. I have heard this before, on Hi-Fi audio tracks, especially on material recorded in EP (6-hour) mode.

If your problem is similar to what I've experienced, then it is not a tracking issue. You can test this for yourself simply by playing the tape using your existing deck and, while playing, use the deck's manual tracking control. My bet is that you won't be able to make the problem go away by adjusting the tracking manually.

So, my first suggestion is to transfer with a deck that doesn't have a Hi-Fi alignment issue (I think your problem is caused by an alignment issue that requires a skilled techician to fix).

The other "solution" (I put that in quotes because it has its own issues) is to switch to the linear audio track (sometimes labeled "normal"). That track won't have this noise. However, if I am right, and this is an EP tape, the bandwidth of the linear track audio is pretty bad (think AM radio), so it will be somewhat muffled. However, you won't have that flutter artifact.

[TONYFRANCE]

First : this is a commercial tape
Second : I tried the manual tracking, and it works

[JVRaines]

VHS hifi audio is very sensitive to tracking. The picture may be great, but if it's a wee bit off, you can get "bats' wings" in the audio.
BTW, VHS linear audio is not as bad as AM radio (16 kHz frequency response versus 10 kHz). I think it sounds bad on a lot of decks because of azimuth misalignment.

[johnmeyer]

VHS hifi audio is very sensitive to tracking. The picture may be great, but if it's a wee bit off, you can get "bats' wings" in the audio.
BTW, VHS linear audio is not as bad as AM radio (16 kHz frequency response versus 10 kHz). I think it sounds bad on a lot of decks because of azimuth misalignment.

I agree when the tape is recorded in SP (2-hour) mode. According to specs, the bandwidth at that speed is indeed 10 kHz. However, if you look at those same specs, when the tape is recorded in EP (6-hour) mode, this drops to only 4 kHz which is pretty close to what you get with AM radio.

I'll stick with what I said earlier about the Hi-Fi alignment being the problem. If it truly was a tracking problem, and only a tracking problem, then the audio and the picture should both be good at the same time as you change the manual tracking. However, if the picture is good while the audio is bad, or vice versa, then the problem is Hi-Fi alignment, and using a different deck is the solution.

Whether or not it is a commercial tape doesn't mean it is going to be better than one you recorded yourself. If you ever looked at the duplication technique for commercial tapes, they either duplicated at faster than real time, or recorded multiple tapes in parallel (on wide tape stock) and then slit them linearly, the length of the tape. Either approach could introduce errors. I think you'd find that if the same material were recorded onto the same tape formulation, one tape at a time, at normal speed, in a professional VHS deck, the results would be better.

[mike20021969]

Whether or not it is a commercial tape doesn't mean it is going to be better than one you recorded yourself. If you every looked at the duplication technique for commercial tapes, they either duplicated at faster than real time...

I didn't realise they could record VHS faster than real time. I know it was common practice with commercial audio cassette duplication though.

[pandy]

VHS linear audio is not as bad as AM radio (16 kHz frequency response versus 10 kHz).

I've had impression that VHS stationary head audio bandwidth ends around 8 - 9kHz and AM radio at best goes up to 4.5 - 5kHz(9 - 10kHz spacing)?

[johnmeyer]

VHS linear audio is not as bad as AM radio (16 kHz frequency response versus 10 kHz).

I've had impression that VHS stationary head audio bandwidth ends around 8 - 9kHz and AM radio at best goes up to 4.5 - 5kHz(9 - 10kHz spacing)?

See my earlier post about VHS linear audio bandwidth. With EP (6-hour) linear audio recording, the bandwidth drops to under 5 kHz.

As for Hi-Fi audio and the need for head alignment to avoid what the OP is calling "helicopter sound," I refer him (and everyone else) to this Wikipedia article:

Videocassette recorder

What you will find at that link is this:

Due to the path followed by the video and Hi-Fi audio heads being striped and discontinuous—unlike that of the linear audio track—head-switching is required to provide a continuous audio signal. While the video signal can easily hide the head-switching point in the invisible vertical retrace section of the signal, so that the exact switching point is not very important, the same is obviously not possible with a continuous audio signal that has no inaudible sections. Hi-Fi audio is thus dependent on a much more exact alignment of the head switching point than is required for non-HiFi VHS machines. Misalignments may lead to imperfect joining of the signal, resulting in low-pitched buzzing.[24] The problem is known as "head chatter", and tends to increase as the audio heads wear down.

[pandy]

See my earlier post about VHS linear audio bandwidth. With EP (6-hour) linear audio recording, the bandwidth drops to under 5 kHz.

Your comment triggered my curiosity - comparison between AM broadcasting and stationary VCR head magnetic recording for audio bandwidth.

[raffriff42]

Whether or not it is a commercial tape doesn't mean it is going to be better than one you recorded yourself. If you every looked at the duplication technique for commercial tapes, they either duplicated at faster than real time...

I didn't realise they could record VHS faster than real time. I know it was common practice with commercial audio cassette duplication though.

They would create a "mirror master" and magnetically print the copies at high speed by direct contact -- this page explains it pretty well:
http://www.otari.com/support/vintage/t710/index.html

[JVRaines]

VHS linear audio is not as bad as AM radio (16 kHz frequency response versus 10 kHz).

I've had impression that VHS stationary head audio bandwidth ends around 8 - 9kHz and AM radio at best goes up to 4.5 - 5kHz(9 - 10kHz spacing)?

My understanding is that the better decks eventually achieved greater than 10 kHz frequency response, an improvement similar to what happened with audio Compact Cassette which was also lo-fi (voice quality) when first developed. AM radio has audio frequency response of 20 Hz – 10 kHz (http://www.radioworld.com/headlines/0045/opinion-39let39s-keep-am-sounding-good39/313449).

[johnmeyer]

When talking about AM radio, I think people are confusing two different things, both of which are measured in kHz. What I am talking about is the frequency response of the audio that you listen to. This is the spec that used to dominate the Hi-Fi equipment market: 20Hz - 20kHz was the typical "Hi-Fi" audio bandwidth.

The 10 kHz several people have mentioned is the channel allocation for North American AM radio. This means that each AM channel has to be at least 10 kHz away from any other nearby channel. This channel bandwidth directly impacts how high a frequency can be transmitted. The relationship is quite simple because Amplitude Modulation is very simple, mathematically speaking (compared to FM, which is actually quite complicated).

With AM radio, the carrier sine wave gets modulated (moved up and down in amplitude) by the audio signal. This creates energy on either side of the carrier, creating what is known as an upper and lower sideband. Each sideband will be above and below the carrier frequency by an amount equal to the frequency of the audio being transmitted. So, for example, if you transmit a 5 kHz sine wave, this will create two sidebands that will be 5 kHz above, and 5 kHz below the carrier. This will completely use up the 10 kHz channel allocation. Therefore, in theory, the maximum audio frequency that can be carried by an AM radio station is 5 kHz. However, because there needs to be some guard against interfering with adjacent channels, and for various other practical reasons, the audio frequencies actually fed to the transmitter are limited to about 4 kHz, the same as the VHS EP linear audio track frequency response.

Here's a link which shows that, at EP speed (6-hour mode), 4 kHz is all you can expect from the VHS linear audio track:

VHS Audio

I spent several years at the microwave test equipment division of Hewlett-Packard, back in the early 1970s when it was still just a test and measurement company, and spent many hours during my first few months playing around with all sorts of signal generators, watching various types of modulation on a spectrum analyzer. It was a wonderful education.

[pandy]

As a person living in Europe i was a bit surprise that AM in US allow 10kHz bandwidth for signal (i.e. with DSB this gives us 20kHz RF occupancy) - most of European broadcasters on LW and MW must strictly follow 10kHz raster (station carer from carrier can be located not closer than 9 - 10kHz i.e. signal bandwidth must be maximum half of it). Live proof on one of the most coolest web pages ever - European real time RF spectrum analyzer - over 29MHz with online demodulation and listening - highly recommended: http://websdr.ewi.utwente.nl:8901/

VHS linear (stationary head) audio bandwidth i assume there is no linear/proportional dependency between bandwidth and tape speed - recorded length wave is more related to head construction (material and how narrow head gap is), size of magnetic particles on tape is another important factor... I can imagine combined head (separate write and read head as combo) + good tape (uniformly distributed fine magnetic particles) with better bandwidth.