Trying to wrap my head around terminology regarding frequency response

[Hammerstone]

...in that, I haven't found a good explanation to just how much signal any given tape deck can record. Can anyone help me out here?

Here's what I'm having trouble with: digital records between 20Hz and 20kHz and nothing else. My personal tape deck is a Teac A-2340RS, and I think I read somewhere that the frequency response for that at 7.5ips goes somewhere to 25kHz, and somewhere under 20kHz for 3.75ips. So does that mean that it stops recording at 25kHz, or that it begins to roll off around that frequency, or that that's all they tested it to?

And is this terminology pretty much standard across the board? For instance, if I record a tape with significant high-freq on a tape deck rated to 25kHz (or more), and play it back through an amp rated to a standard 20Hz-20kHz, am I losing all frequencies over 20kHz?

I hope I'm getting my questions across. I've been all over this board and haven't found much that hasn't made me more confused, so if there are websites out there explaining this, please post some, or if anyone could give me a good explanation, I would be very grateful.

 

[The Ghost of FM]

All you have to do to figure this stuff out is to look at a frequency response chart which will instantly show you where the highs, lows and everything in-between rolls off the charts. Some decks do it gradually and gracefully, and others drop off like a cliff.

Generally speaking, all frequency response specs are completely useless unless they are accompanied by a +/- db rating. As an example; If a company claims that their tape recorder will record and reproduce a signal from 30-20,000 Hz, plus or minus 2 db, we know that that's a pretty good spec. But if that same range is qualified by a plus or minus 6db spec, we can assume that at 20Khz, the levels will be much lower and therefore, not as good/flat.

In digital's early days, they used to provide the +/- qualifier number to that spec, but as all of them were pretty close to dead flat line, they stopped giving out that part of the spec. But with digital, beyond 20Khz, there is a virtual cliff drop off response unlike analog, which has a slippery slope instead.

Hope that helps.

Cheers!

 

[The Ghost of FM]

Also, regarding frequencies above 20 KHz, odds are, if you're over the age of 10 or 12, or have played in a band for a few years or worked under noisy conditions, you'll never hear them anyway.

Cheers!

 

[bouldersoundguy]

...in that, I haven't found a good explanation to just how much signal any given tape deck can record. Can anyone help me out here?

Here's what I'm having trouble with: digital records between 20Hz and 20kHz and nothing else. My personal tape deck is a Teac A-2340RS, and I think I read somewhere that the frequency response for that at 7.5ips goes somewhere to 25kHz, and somewhere under 20kHz for 3.75ips. So does that mean that it stops recording at 25kHz, or that it begins to roll off around that frequency, or that that's all they tested it to?

It rolls off. Generally it's specified what the level range is (for example ±3dB), so that 25kHz is still within some specified range.

And is this terminology pretty much standard across the board? For instance, if I record a tape with significant high-freq on a tape deck rated to 25kHz (or more), and play it back through an amp rated to a standard 20Hz-20kHz, am I losing all frequencies over 20kHz?

Unless you're a dog I wouldn't worry too much about "losing frequencies" above 20kHz. And the 20-20k spec is also referred to some specified level range so it doesn't fall off a cliff, it rolls off.

 

[Hammerstone]

All you have to do to figure this stuff out is to look at a frequency response chart which will instantly show you where the highs, lows and everything in-between rolls off the charts. Some decks do it gradually and gracefully, and others drop off like a cliff.

Generally speaking, all frequency response specs are completely useless unless they are accompanied by a +/- db rating. As an example; If a company claims that their tape recorder will record and reproduce a signal from 30-20,000 Hz, plus or minus 2 db, we know that that's a pretty good spec. But if that same range is qualified by a plus or minus 6db spec, we can assume that at 20Khz, the levels will be much lower and therefore, not as good/flat.

Thanks for the info. The only problem with frequency response charts that I've seen is that they all tend to stop at 20kHz. Even this very informative article doesn't really answer the questions I'm asking, though it does seem to indicate that a tape deck will record past the limit of human hearing. But how far does it go? I take it then, that if a manufacturer rates a product only going to a certain frequency (usually 20kHz), that they generally don't publish what happens above those frequencies, but something's happening up there. I remember reading articles from MoFi (not that I am able to find them now) that discussed extreme high-frequency but besides that, where else should I be reading?

Anyone?

Unless you're a dog I wouldn't worry too much about "losing frequencies" above 20kHz. And the 20-20k spec is also referred to some specified level range so it doesn't fall off a cliff, it rolls off.

I'm not worried much about my being able to hear the high frequencies, and although I haven't been tested, I'd say I have pretty good hearing. But isn't it one of the main argument points of analog in general that those frequencies you can't hear, that digital cuts out, are part of what makes analog sound better?

 

[The Ghost of FM]

... isn't it one of the main argument points of analog in general that those frequencies you can't hear, that digital cuts out, are part of what makes analog sound better?

I don't think that was the main argument of analog over digital, or at least not the enduring ones which focus more on analog's ability to soft saturate and produce more musical harmonic distortion rather then rather ugly inter-modulation distortion which brings out a panic response that something is about to blow up. That and the un-flat bass bump that adds that warmth quality that also gets associated with analog recording.

About what's going on above 20 KHz when its rolling off on a curve rather than off a cliff is that the top end "air" tends to remain more in phase which will preserve things like reverberence and maintaining a more cohesive stereo imaging presentation to the listener. But, because we also know that almost no one has the exact same hearing response in our ears or the exact same sized and shaped heads, we all seem to hear things just a bit different than each other. So while one listener may claim to hear some of those qualities that I described about what goes on above 20Khz, another person may not catch that stuff at all. And that also is related to how some people are naturally pitch perfect when they sing and others couldn't stay on key to save their life. So there's a real mental process going on to appreciate these differences and that can include the placebo effect where some people may trick themselves into hearing or not hearing certain things because of expectation and reputation for a given brand or model of a piece of gear that got high praise elsewhere. Basically, a bit of science and a bit of the human factor mixed together to ensure endless debate and controversy.

My 2 cents.

Cheers!

 

[bouldersoundguy]

I'm not worried much about my being able to hear the high frequencies, and although I haven't been tested, I'd say I have pretty good hearing. But isn't it one of the main argument points of analog in general that those frequencies you can't hear, that digital cuts out, are part of what makes analog sound better?

If you can't hear it it doesn't affect the sound. It's the part of the sound you can hear that matters. That is, the frequency response deviations/variations and harmonic distortion are what give analog its sound.

 

[Hammerstone]

Hmmmm...not that I'd know all about it myself, but I thought a good part of that "harmonic distortion" was due to the complexities of higher frequencies (outside of the range of hearing) interacting with lower frequencies. I'm sure I've read articles to that effect. Why else would Mobile Fidelity, of all companies, stress the importance of high-freq like they do?

 

[Chilljam]

Why else would Mobile Fidelity, of all companies, stress the importance of high-freq like they do?

I'm not sure if you are being sarcastic or not here... Of course it is in their interest (from a business perspective) to argue that frequencies outside of the hearing range do contribute to the sound as they work with vinyl and SACD, both of which store the extended high frequencies unlike CD or MP3.

I agree though that if your speakers are reproducing frequencies above 20kHz then, even though they unaudible, they are interacting (phasing) with the audible frequencies. I also think that there are about a million other things to worry about in the recording chain than how well you are recording inaudible frequencies.

Actually, you could test your machine yourself - grab a signal generator that has frequencies above 20kHz and record them on the tape at 0VU and see what levels you get on playback.

 

[Chilljam]

double post please delete

 

[Hammerstone]

Thanks for the ideas. I would wonder if my personal speakers *would* generate signals over 20kHz, as they're not the best in the world, and neither is my current amp...which was kind of one of my other questions. Guess I can find out! I'm starting to feel like I've opened a can of worms here...

...

So I've done a slight bit of fooling around, and come to the conclusion that I really REALLY need to calibrate my deck, AND align the heads maybe (wow, really should have done that before I started recording)...each track was at a different level. Other than that, I'm not sure just what I accomplished.

It seemed that the curves were all over the damn place, just judging from the preamps. Everything rolled off somewhere between 19- and 20kHz. The highest peak seemed to be somewhere around 1kHz. Off the tape, at 7.5ips, there didn't seem to be as much head bump as I expected, and things rolled off rather more gradually than with the preamps. Hmmm...lots to think about...