Quantcast VHS Frequency Response Tests - digitalFAQ Forum
  #1  
04-28-2014, 07:38 PM
Belmont Belmont is offline
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Hey guys, how the heck ya doin'? Remember me? Been years since I've been here (long story short, I transferred what I needed and all that). However, recently I've been doing some audio work, and I got curious as to what VHS's actual frequency response is (heck, I vaguely recall promising someone I'd get around to testing it).

So the other night, I made whipped up a quick test track to put VHS audio to it's paces (you could also possibly use this to test your sound system, if it's a stereo one). It's pretty straightforward-2 30-second sine-wave sweeps from 20-20,000Hz (one is linear, and the other logarithmic), a short burst on each channel (useless for linear audio), and 3 musical pieces that have lots of bass/treble or require a large dynamic range. Unfortunately, I lent my good JVC VCR to my brother (he needed it for his workplace last Halloween and I haven't seen it since ), so I'm left with the crummy Toshiba VCR/DVD deck. Ah well, better than nothing, and probably for the better since so many still use those confounded contraptions to transf-bah, I was bored and there's really nothing better to do on a Thursday night

So anyway, I picked three music tracks that I felt would push VHS audio to the limit. I'll confess that I mainly used vinyl sources, since I didn't want any compression or low-bitrate audio skewering the results.
*The first is Wagner's Liebestod, played by Virgil Fox on the famous Macy's Grand Court Organ (the 2nd biggest in the world, I might add), from a 1964-ish audiophile LP. While it can't stack against the real thing (I've heard it several times myself-it's freakin' breathtaking), it still has lots of very deep and very high frequencies, and goes from just about nothing to maybe 50% of what it can do, so it's a good test of frequency and dynamic range.
*The second is Radioactive, by Imagine Dragons. I'm pretty tired of this song being played on the radio 24/7, but the throbbing dubstep-esque bass and overdriven vocals balanced by delicate acoustic guitars makes a good test subject.
Unfortunately, I had to rely on the Youtube copy, which is probably mangled by compression, but it still sounds okay to my ears. A friend of mine has the song on vinyl, and I daresay the Youtube copy sounds better (then again, his record player's a Crapsley ).
*Lastly, I found an old HiFi sampler record from the mid-50s in the basement (we have a lot of crap from my late-grandfather's massive estate in the storage room). It had various generic things on it (a banjo duet, an electronic organ solo, and tired Vaudeville numbers), and touted audio ranging from 16Hz to 20000Hz (ha!). I decided to give it a play and found an annoyingly catchy jazz medley, with a strong string-bass and some pretty wild drumming. I guess it works as sort of a middle-of-the-road test subject.
-All sources were normalized to -3dB

The Results:
*Linear audio was pretty horrid. On the tone sweeps, it did this very odd thing were the audio seemed to just go back and forth when it supposed to be at the high end. Incredibly strange.
*On HiFi mode, instead of the audio sweeping back and forth, the audio (and video) started to crackle. I'll confess straight away that I used the end of an old Fuji T-160, so the tape's pretty suspect.
*There was literally NO difference between SP and EP audio in HiFi mode. Now, linear/mono, on the other hand...
*Surprisingly, HiFi mode was flat all the way to 20kHz. However, I think I detected some compression, although I'll admit I've never been good at detecting mild compression.

I'd be pretty interested if anyone else would bother doing this same experiment and posting their results, because it probably does vary between VCRs.

Overall, I'd say that, in mono mode, you can do away with anything below 70Hz and above 10kHz in SP mode, and anything below 100Hz and above 6kHz in EP mode. OR, if you wanted to, you could possibly create an inverse of the frequency-response curve and use that to perhaps restore the audio back to a flat-ish response (after de-noising, I hope!). I'm actually going to try that tonight to see how it goes.


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  #2  
04-28-2014, 10:20 PM
NJRoadfan NJRoadfan is offline
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A Dolby noise reduction application available for linear track audio. It was offered on VCRs and pro editors that used dual linear (stereo) audio. This was mostly since the width of the track was reduced and they had to find some way to improve the audio quality. The normal linear track had a frequency response similar to a compact cassette. Keep in mind that back in the 1970s when VHS and Betamax were developed, TV audio really wasn't high quality or in stereo, so it sufficed. Stereo TV audio broadcasts didn't air until 1984 and became widespread shortly thereafter.
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05-06-2014, 04:23 PM
Belmont Belmont is offline
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Was the Dolby system ever implemented in regular VHS recorders?
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05-06-2014, 06:39 PM
NJRoadfan NJRoadfan is offline
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The only consumer machines with Dolby NR were linear stereo models. Here is an example of one, note the Dolby logo on the front panel. http://vintageelectronics.betamaxcol...elpv-1563.html

There were also models with both linear stereo and Hi-Fi stereo, such as this: http://vintageelectronics.betamaxcol...lvh5846xe.html

I own the same model deck, but it needs some parts and work to get up and running again.
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05-06-2014, 08:07 PM
Belmont Belmont is offline
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That's a real monster of a deck!

You know, I find it interesting how that same boxy aesthetic that you see in old '80s cars was also found in the electronics of that time (and even today, to an extent). Same thing goes for that super-curvy/ergonomic style that dominated the '90s (which I've never cared for, tbh ).
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05-09-2014, 06:47 PM
dpalomaki dpalomaki is offline
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FWIW: The AG-1970/1980 specs call for 20-20K Hz, 75 dB S/N, 90dB dynamic range for the Hi-Fi audio,
The normal linear track is about 50-10K Hz, 40 dB S/N. (tape speed 33.3 mm.sec / 1.31 ips)
(dB down was not specified)

On the other hand, audio cassettes move tape at about 1.86 ips
And reel-to-reel 1/4" mag tape uses 3.75 and s 7.5 ips for most consumer gear.

SPL/EP tape speed is 11.1 mm/sec) - not very fast. We can expect the linear track audio to be pretty bad, a bit below AM radio quality, but arguably suitable for a TV set with a 3 1/2" speakers.

I once had an early 1980s vintage RCA portable VCR with a docking station - it had stereo linear tracks. Long gone now
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