Get rid of tape hiss?

mjr

mjr

ADD -- blessing and curse
I have a Yamaha 4-track. I read here in the tutorials about using the high-speed tape speed, and turning off the DBX (I usually keep it turned off anyway). My question is, how can I get rid of tape hiss so my recordings sound better once I get them on my computer & then on CD?
 
Turn the dbx back on. That's what it's for.

Tape hiss is random noise. There's no obvious way to eliminate it. You can EQ it out, but you'll EQ out a lot of the character of your signal too.

(A small clarification to my "turn the dbx back on" solution: don't turn it on when playing back tapes recorded with it off. Turn it on when you record from now on. Unless you hit the tape absurdly hard).
 
So, would I leave it on when I'm recording from my 4-track to my computer as well?
 
First off, tape hiss isn't "random noise". It is quite consistent every time to press play on the machine. It is caused by the tape running over the tape head. Faster tape speeds move the frequency range that the hiss happens at up higher. Cassette's run at relatively low speeds, thus, the tape hiss is well in the audible range for all humans. About the slowest speed that tape hiss is not audible is 30IPS (inches per second), and you won't find any cassette players/recorders that run tape that fast. Thus, you have noise reduction.

Noise reduction is a sort of compression scheme that only compresses the lower frequencies while recording to tape. By doing so, you are able to record much hotter levels of high frequency to tape which is what helps eliminate tape hiss. When a recording that was recorded with some type of noise reduction ("encoding") is played back, the "decoder" expands the bass back out so that the overall frequency range is mostly unchanged from where is started out. The success of the noise reduction in not only eliminating hiss, but also not drastically changing frequency response is dependent of how well the manufacture built the noise reduction circuit as well as many other factors. But let's say for the sake of arguement that most noise reduction scheme's on newer recording equipment works well enough for the price point of the product. While the dbx on your unit is FAR from state-of-the-art noise reduction, your unit is far from needing higher quality noise reduction, because traditionally, 4 track cassette recorders are used for demo purposes. On a demo, sacrificing a little frequency response, or having a bit of tape hiss even WITH noise reduction on is acceptable.

Anyway, if you RECORD with noise reduction, you need to PLAYBACK with noise reduction too. You will notice that music that was "encoded" with noise reduction with actually sound like it has MORE hiss if you play it back without the same type of noise reduction "decoding" it.

Now, it is debatable, and subject to much arguement whether noise reduction on a cassette helps or hurts the overall sound. Try recording both ways to see which offers the most benefits to your recordings.

A little tip though. Most "demo" recordings always seem to suffer from overhyped up low midrange frequencies in it. While you are tracking, you need to really try to clear this up because all that lower midrange is eating up headroom on the tape, thus, you cannot achieve as hot of recording levels as you would like. The hotter the signal you can record to tape the less you will notice tape hiss is the rule. So, try to achieve the hottest levels possible while tracking to cassette tape to overcome tape hiss. If the tape hiss is still unacceptable, then employ your noise reduction to help reduce tape hiss.

Good luck.

I have had some luck using software plugin's to eliminate tape hiss on recordings transferred to a computer. Steinberg's Denoiser VST plugin seems to work quite well at eliminating tape hiss without changing the sound of the music very much. I have done a little bit of audio restoration on cassettes in the past, and all the clients were quite pleased with how Denoiser worked. So, you might check it out, along with the many other noise eliminating plugin's that are available.

Ed
 
Great explanation Ed.

General wisdom is that it is better to record at most mildly
(+2 db or less) into the "red", and use the DBX noise reduction
like sj said. As you may know, mjr, it's always best to clean the
heads before and after each recording session, along with
periodically "demagging" the heads.

Also, if you know in advance you're going to boost any high end
EQ, do it BEFORE the signal hits the cassette unit, not after.
Otherwise that will boost your hiss unnecessarily.

Chris
 
Just a few notes:

sonusman said:
First off, tape hiss isn't "random noise"....
Click to expand...

Well, I don't think we disagree wildly here, but it is random in the sense I meant. It's caused by the various magnetic "domains" that aren't flipped a specific way (north or south) being flipped various random ways. For a sort of stretched analogy, picture a road made of little 1" x 1" tiles -- about half of them are randomly pushed up a few inches. If you drive your car over it, your tires will go bu-bu-bu-bu-bu and make a noise. Although the tiles are pushed up randomly, the noise will have a characteristic sound and approximate frequency. If you go faster, the frequency will increase. At a given speed, the frequency with which you hit a raised tile will vary -- you'll hit little stretches that might run hi-lo-hi-lo or hi-lo-lo-hi-lo or even hi-lo-lo-lo-lo-hi, but -- the law of average being what it is -- it won't vary a whole lot and a particular odd frequency won't continue (hi-lo-lo-hi-lo-lo-hi-lo-lo-hi-lo-lo-hi-lo-lo... doesn't happen).

Tape hiss is random, even though it has a characteristic sound. The (probably wildly inobvious) point I was making is that because it's random, the precise shape of the signal isn't predictable and there's not an easy way to eliminate it by mixing it with phase-inverted "standard" tape hiss or something.

Incidentally, a cassette player that runs at 30 ips would play one side of a C-60 cassette in a little under 2 minutes. Cassette decks don't even rewind at 30 ips!

... Noise reduction is a sort of compression scheme that only compresses the lower frequencies while recording to tape. By doing so, you are able to record much hotter levels of high frequency to tape which is what helps eliminate tape hiss....
Click to expand...

Not quite, although I think the overall concept is right. Dolby is frequency dependent (exactly how varies with the type of Dolby), as is dbx Type II, which is what would be in a cassette deck (dbx Type I, as found in a reel-to-reel deck, is a straight non-frequency-dependent compression / expansion scheme). But I believe it's the other way around: dbx Type I affects the high end more, and mostly leaves the low end alone. Fooling with the dynamics of the low end in combination with a recorder with somewhat unpredictable and variable low-end response causes encode / decode mismatches.

... if you RECORD with noise reduction, you need to PLAYBACK with noise reduction too. You will notice that music that was "encoded" with noise reduction with actually sound like it has MORE hiss if you play it back without the same type of noise reduction "decoding" it....
Click to expand...

Yes.
 
Leave the geeks to their word games... :D

dbx does a pretty fucking good job of getting rid of the hiss on a cassette tape. Of course once you're spoiled by a decent digital recording or a decent tape machine you WILL start to hear annoying hiss that you never would have noticed before.

And it's also dependent on the type of program material that you're recording. Quiet acoustic stuff will accentuate hiss and loud electric rock will mask it.

As to dbx:
Just be sure to record WITH it ON and play back WITH it ON.

Other combos won't work.

Oh- and use some decent tape. And keep your heads clean.
 
and to add my penny's worth...............

......................a hi-lo pass filter can also assist in the reduction of hiss. I have an old Beh'gr Intelligate that contains a Hi & Lo filter option that comes in handy on analog rec'dings.
 
you should record and playback with the noise reduction on! recording without it and flipping it on during playback will be horrendous!...wait, that was already said...also don't be afraid to go in the red! A hint of analog distortion is pretty cool.
 
chessparov said:
General wisdom is that it is better to record at most mildly
(+2 db or less) into the "red", and use the DBX noise reduction
like sj said.
Click to expand...

My experience with Yamaha casette portas say that you should:
1. Buy good quality tape
2. Hit the tape as hard as you can without distortion
3. Use dbx.

I've later learned that this probably gives me some tape compression, which probably is why it sounded good. YMMV.

My MT2X sounded awesome for being a casette porta, IMO.
 
The "+2 db" comment was largely based on comments by people
like Peter McIan. My understanding is that if you go into the red at
+2 it comes out roughly equal to +4 once the dbx is decoded.
He seemed to think the heads on a cassette multi-track were too
small to hit above that dependably without risking too much distortion.

Chris
 
an answer...

Since mrj is a newbie i am going to try a little more basic approach to removing the hiss..the technical debate over noise reduction schemes and the level to record at might be doing more harm that good (depending on mrj's experience with those sorts of things, of course). The best suggestion so far was the first..of course..don't record to tape in the first place :). What you might want to do is use your 4 track as simply a mixer and run it straight into your computer, provided you have a program on your computer that will be able to edit 4 tracks or so. I have heard on this board people talking about a couple free multitrack recorders which certainly aren't be the best, but worth a try. if you DO have a recording program then once you record it in just touch it up with a lil noise reduction and go on to the next track. if you don't have a recording program already and the free one doesn't offer decent noise reduction then I have only wasted your time :)

have a nice day!

dlv
 
Have any of you guys done the "emphasis/de-emphasis" thing?

You know where you boost the high end EQ going into analog tape,
then reduce the high end EQ by the same amount when you mix down.
That has the effect of reducing hiss even without DBX.
(although using dbx in addition is better)

Chris
 
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