Distortion vs EQ

[magiccarpetride]

I am not a sound engineer, so my understanding of the subject matter is extremely naive. But I am getting mighty confused with, what to me seems like a regular conflation between terms 'distortion' and 'EQ'. I would appreciate it if someone could set me straight in these matters.

We often hear how vinyl reproduction adds certain characteristic distortion which then contributes to our assessment that vinyl somehow sounds different than digital reproduction. But my question is: is it distortion, or is it EQ that the turntable appears to be adding to the original signal?

Let me put it this way: I'm a musician, and I like to overdub myself in my home studio. I track myself playing, and then I edit the tracks in Protools. What I often end up doing is messing a bit with the EQ, increasing some frequencies, reducing some other frequencies a bit, etc. So am I actually adding distortion to the original signal? I may not like how the microphone was tracking my instrument, or my voice, so I need to edit it. But as the author, I don't see it as adding distortion to the signal. I see it as polishing the recording so that it sounds the way I like it.

So is a turntable then doing the same thing? Is it polishing the original signal to make it sound more appealing to us? And of course, the better the turntable/plater/tonearm/cartridge/phono/interconnects combo is, the more pleasing, the more satisfying this EQ-ing appears. But why do we then refer to it as 'distortion'?

[walpurgis]

EQ is not distortion. It is alteration of the signal amplitude. Distortion is deviation from the signal form. Added noise is an imposed distortion.

[struth]

that avatar has to go Geoff. Im getting you mixed up with too many folk now... I'm old n confused enough :doh:

[Rothchild]

A turntable may well be adding distortion (normally a flattening or 'clipping' of the 'upper' part of a wave (as in the bit towards the top of it's amplitude curve) it might also be having frequency specific amplitude effects (which is what eq is).

Distortion

http://www.electronics-tutorials.ws/amplifier/amp12a.gif?x98918

Harder to visualise EQ but a graphic does it well, here each slider just controls a specific frequency from 31Hz on the left hand end to 25kHz at the right

https://www.proaudiocentre.com/blog//wp-content/uploads/2012/10/band.jpg

[Firebottle]

Good post ^^

EQ could alternatively be termed 'tonal adjustment'. For vinyl playback the EQ is very specific, RIAA usually, to make the best of the limitations of recording onto the vinyl media.

Distortion generally adds new harmonics to the signal, in the case of the clipped waveform above they will be mainly odd order and sound 'wrong' to our ears.

:)

[RothwellAudio]

It's a good question and I have wondered myself why EQ doesn't create distortion when it clearly makes the output signal different from the input signal. Well, it does - but it's known as linear distortion. The "bad" stuff is known as non-linear distortion.
Here are a couple of articles about it.

http://www.nti-audio.com/en/news/let%E2%80%99s-clear-up-some-things-about-distortion%E2%80%A6.aspx

http://www.audiomasterclass.com/the-difference-between-linear-and-nonlinear-distortion

[dimkasta]

Well EQ is a type of distortion. The difference is that it is added deliberately and in a controlled manner, to essentially become part of the signal itself (for example the master)
In direct contrast to let's say harmonic distortion which cannot be controlled outside the design or build process (usually), and is unwanted (usually)

Now on your question about turntables and their character... This is a topic that probably has started many threads and many flames.
My opinion is that saying that turntables have a character because they add distortion is an oversimplification, an unjust generalization and a bit silly because it suggests that other devices do not add distortion.

All devices add some kind of distortion. How much and of what type depends on the design, the implementation and actually can even differentiate between two samples of the same model if the manufacturing process does not strictly select and match parts to very low tollerances.

[RothwellAudio]

Well EQ is a type of distortion. The difference is that it is added deliberately and in a controlled manner, to essentially become part of the signal itself (for example the master)
In direct contrast to let's say harmonic distortion which cannot be controlled (usually) outside the design or build process, and is unwanted.
This isn't quite true. Aural exciters are used deliberately but they are not adding linear distortion, they are adding non-linear distortion. The basic function is to operate on frequencies above a certain cut-off frequency, distort the waveform to add harmonics and then blend the distorted signal in with the original signal. The effect is to add some sparkle to the sound.
In reality aural exciters are more complicated than the crude explanation above (or should be :) )
https://en.wikipedia.org/wiki/Exciter_(effect)

[dimkasta]

Exciters are again a processing tool that is deliberately and conditionally applied to the signal to become part of it (for example the master)

I referred to unwanted and uncontrollable harmonic distortion like that created by semiconductors in an amplifying stage.

[RothwellAudio]

But my question is: is it distortion, or is it EQ that the turntable appears to be adding to the original signal?

I think I may have misunderstood the OP's question, or overlooked the nub of it (above).
The turntable shouldn't be EQing the signal, though MM cartridges certainly don't have the flattest frequency response ever seen. Some distortion is inevitable though. The main types of distortion in vinyl playback are tracking distortion and tracing distortion.

[dimkasta]

There could be some EQing in cases where the RIAA implementation is a bit off or does not match the RIAA used by the engineers that did the mastering. But it is not something consistent that can be considered a characteristic of all turntable based systems.

A distortion that can be consistent between all turntables is noise. And the tracking/surface noise (not clicks, pops etc) can create a dithering effect.

[alphaGT]

Vinyl stereo records first introduced in 1948, use a system of equalization called RIAA, forget what that stands for, but some kind of association. Vinyl records have certain limitations, so engineers figured out a way around them. When a tape recording is cut to a record, the high frequencies are very tapered off. And low bass frequencies would have grooves so wide you couldn't fit them on the record. So, they came up with a solution. They cut the bass frequencies way down. And they pump the high frequencies way up! Using an equalizer. Then they cut the master record, and make copies to be sold. Then, the cartridge picks up the music off the record, and it is sent through the RIAA equalizer to undo the changes made before the record was cut, it cuts the treble and pumps up the bass, make it normal again. This way, they can get a far greater frequency range onto a record. Old 78 records had an equalization method too, but it was just on the recording end, there was no further EQ'ing on the playback end.

I realize this has little to do with the original question, but I wanted to point out that whether we think we are using any EQ or not, it is definitely being used. Using EQ doesn't necessarily distort the original wave form, no more than turning the volume knob up and down, it's only turning the volume up and down on selected parts of the original wave form. While the wave form has changed, it's still not what they usually mean by distortion. I'm not sure if this helps or hurts?


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[Rothchild]

Vinyl stereo records first introduced in 1948, use a system of equalization called RIAA, forget what that stands for, but some kind of association.

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Yup the 'Recording Industry Association of America' specify the emphasis and de-emphasis curve used for cutting records works as you've described, but for the sake of some amount of historical accuracy, it wasn't introduced or widely used until 1954 (and even then it took a while longer to establish itself). There are apparently at least 100 'standards' that were used by different labels and cutting houses prior to that.

I kind of agree with the semantic twist that a couple of poster have put on this insofar as a deliberate change of frequency content using an EQ could be considered EQ whereas a frequency shifting effect caused by equipment not having a completely flat frequency response across the audio spectrum could be interpreted as distortion (an unintended deviation from the actual content on the source).

[337alant]

I agree with AlphaGT and Rothchild, changing EQ is not adding distortion it is changing the amplitude to a sign wave at a given frequency and that is part of the RIAA process anyway.
Distortion in Vinyl play back mainly comes from miss tracking caused by poor arm / Cart geometry or set up so its very important to get that set up correctly first.
It is also possible that harmonic distortion is unintentionally added by a poor quality phono stage adding a bloom to the sound ? remember that MM ads approx 45dB and MC 60dB of gain to a signal so any distortion in the signal path is amplified up to a thousand times :eek:

When they talk about about vinyl warmth I just think that is a product of the frequency response produced by the RIAA correction and the Cartridges own Voice (and cartridge loading) plus the distortion in the phono circuit which does not produce the ruler flat frequency response that you get from digital.
Reel 2 Reel also produces a hump in the bass and at low speeds a rolled off HF but it still sounds great never the less

I think that we also have to accept that certain types of distortion do sound good to the human ear and a perfectly pure and flat frequency response can sound a bit flat and sterile
Also remember the every guitar sound we hear on a song has already had all sorts of distortion sounds intentionally added to make it more attractive to the music being played
Alan

[alphaGT]

Thanks Marc, it's been a long time since I read up on that stuff. And it's partly responsible for the lack of bass in early vinyl records. I recall a super expensive phono preamp that has multiple curves to choose from, it had a Decca curve, a few others, and the RIAA. I can't recall the make, but the reviewer wondered why they bothered to include it, but I guess if you own old Decca records, or whatever other old recordings, you might want it?

As has been already pointed out, every single piece of the playback chain introduces distortion. Even CD players, reel to reel decks, and digital file servers all introduce some kind of distortion.

Back in the days when jitter was big news in new DAC's and CD players. There was argument that the nature of analog distortions were at less noticeable frequencies, and even the tiniest amount of jitter was noticeable because it was in a more irritating place. Forgive my lack of technical detail, I'm working from memory. Anyway, my point is there are many kinds of distortion. Intermodulation distortion, Harmonic distortion, even order and odd order, EMF RFI distortions, just all kinds! It's truly amazing we can enjoy reproduced music at all!


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