What is "phase smear"?

[rasputin1963]

In acquainting myself with linear-phase EQ'ing, I have encountered the expression "phase smear".

 

What is this phenomenon? What is getting "smeared", exactly?

 

And how does a linear-phase EQ eliminate or reduce phase smear?

 

 

Thanks, ras

[Kiwiburger]

Think of an audio waveform as consisting of sinewaves with a series of harmonics (higher frequencies sinewaves) which are locked into a synchronised time relationship.

 

Now imagine what happens when your run that waveform through a bunch of capacitors and/or inductors ... which is what an analog eq is comprised of. The basic principle of an eq filter circuit is that low frequencies find it difficult to pass through a capacitor, and high frequencies find it difficult to pass through an inductor.

 

What tends to happen is that the higher frequencies get slowed down, and this means they lose their perfect synchronised time relationship with the fundamental, and other harmonics.

 

Instead of the harmonics arriving at your ear with crisp definition, they get smeared about in the time domain. Actually, it can sound good for some sounds. You sometimes want an eq to sound like it's doing something, right?

 

The thing about digital eq is that you can do something completely artificial, and boost or cut frequency bands without affecting the phase relationship. Eq algorithmns are still vulnerable to phase shift, but what you can do is split the sound into chunks and process them twice. Say you want a 6dB boost, what you do is boost the chunk of audio 3dB. Some phase smearing will occur. Then you reverse that chunk of audio, and boost it a further 3dB. Some smearing will occur, but it is now reversing the phase smearing that first took place. Reverse the audio again, and you have your 6dB boost with zero phase smearing.

 

Something like that - that's a fairly crude explaination.

[UstadKhanAli]

Originally posted by rasputin1963 In acquainting myself with linear-phase EQ'ing, I have encountered the expression "phase smear". What is this phenomenon? What is getting "smeared", exactly? And how does a linear-phase EQ eliminate or reduce phase smear? Thanks, ras

 

You've been reading Monster Cable ads, haven't you?

 

"High velocity of propagation reduces time smear."

[Ethan Winer]

Ras,

 

 

It's a marketing term meant to scare folks into buying overpriced hardware and software.

 

Seriously, phase shift is benign, even in large amounts. The only time phase shift is audible is 1) when it is changing, 2) if the amount of shift is different between the left and right channels, and 3) if you combine original and shifted versions of the same signal. Phase shift is necessary for equalizers to work, and it is not harmful. Here's a little more:

 

www.ethanwiner.com/EQPhase.html

 

--Ethan

[blue2blue]

I dunno, Ethan... can we really trust a guy who uses "mike" for "mic"?

 

 

 

 

[Mind you, I'm all for miking something. And I guess you could then ask me why, in a half hour or so I'm going to be getting on my bike and not my bic... but these little distinctions... it is what separate us from the rest of the animals, right? :D ]

[Ethan Winer]

> I'm all for miking something ... getting on my bike and not my bic

 

Exactly.

 

There's a saying, "If 50 million people say a foolish thing, it's still a foolish thing." So by extension, if 50 million people spell it "mic" that still doesn't make it right. Micing is what my cat Bear does.

 

--Ethan

[blue2blue]

IF it's any consolation, Ethan, my metropolis's world-famous fishwrapper, the LA Times, had an article today on "open-mike" nites... I mean nights.

[rasputin1963]

This little splitting of hairs reminds me of the great Hollywood makeup artist called Perc Westmore... No, it wasn't "perk". It was to be pronounced "purse" (for Percival, I'm guessing?), but you wouldn't know it from looking at the credit rolls of 1940's movies.

 

Also remember in S.J. Hinton's novel THE OUTSIDERS, the goody-two-shoes boys were called "the soc". And here, "soc" was short for "the social types" and thus to be pronounced "sowsh".

 

I don't have any problem with "mike" and "miking".

[UstadKhanAli]

I don't even know about the "micing" and "miking" bit. A while back, someone "corrected" me on rec.audio.pro because I was using "miking". I then also noticed that most of the magazines I saw used "micing". So I figured that might actually be correct and started writing "micing".

 

~~~~~~~~~~~~~~~~~~

 

1. Since we are "splitting hairs", I figured I'd look up www.dictionary.com:

mike1? /ma?k/ Pronunciation Key - Show Spelled Pronunciation[mahyk] Pronunciation Key - Show IPA Pronunciation noun, verb, miked, mik?ing.

Great. Dictionary.com has no listing for "micing", by the way.

 

~~~~~~~~~~~

 

2. Merriam - Webster online:

Inflected Form(s): miked; mik

[Ethan Winer]

Ken,

 

 

As I was saying, if 50 million people ...

 

 

--Ethan

[UstadKhanAli]

I can be biking

I can be miking

I can not bic

But I can flick my bic

[UstadKhanAli]

Originally posted by Ethan Winer Ken, As I was saying, if 50 million people ... --Ethan

 

Well, that may be true, but I've heard 50 Million Elvis Fans Can't Be Wrong!!