NOISE CANCELLATION VS. NOISE ISOLATION

When we shop for a pair of headphones / earphones, along with the exorbitant price we come across terms such as "Active Noise Cancellation" or "Passive Noise Cancellation / Noise Isolation" and more often than not we tend to get bombarded with such fancy terms. So without further ado, let's get it sorted.

We will be mainly looking at two main aspects i.e. the design and the working of each type.

1. Passive Noise Cancelling / Noise Isolating Headphones

This deals with only the physical aspect of blocking outside noise from entering our ears, it isn't some "technology" as such. The efficiency depends on the kind of padding that is provided by the headphone and also, how well it fits on our ears. There isn't much going on here except the padding physically blocking out the ambient noise. This will suffice in an environment where there isn't much of disturbance.

The Sony MDR 1RBT is a circum-aural closed back headphone that provides excellent cushioning which helps in blocking out the ambient noise thereby providing the listener a peaceful listening experience. (click here to know more about headphones)

Since the working doesn't involve any special technology, these less sophisticated headphones are usually more affordable than the ones with ANC technology. Now let's take a look at how ANC headphones work.

2. Active Noise Cancelling (ANC) Headphones

Noise cancellation is where things get a little bit complicated as there is an interesting process going on here, we'll go into this in detail in a bit. But to put it in a simple way, the headphones are equipped to produce an inverse wave (w.r.t original sound signal) so that the signal containing the noise gets cancelled.

1. The Bose QC20i noise cancelling earphones

If closely observed (in Fig.1), one can see that there is a microphone that is present (the little pores) on the earphones, the microphone detects the kind of noise that is prevalent in the environment and sends this information to the circuitry present inside. The circuitry then produces the exact negative signal (Fig. 2) which is fed to our ears (Destructive Interference). When this happens most of the outside interference is cancelled and results in only the desired audio signal being fed into our ears.

2. This picture depicts destructive interference. Let's assume A1 to be the original sound signal & A2 to be the exact negative (180° out of phase) signal, then the net result (A1 + A2) will almost be zero.

Conclusion

While the headphone removes most of the unwanted noise, it should be kept in mind that noise cancelling doesn't eliminate the background noise it only removes the constant/low frequency noise that occurs while traveling in a train or the buzzing sound of many people talking. It is suitable for people who travel a lot on regular basis and not for people who are extremely particular about the clarity as it cancels out some of the low frequencies and it also requires a (rechargeable) battery which is not intended for people who are going to use their headphones in a studio. Last but not the least, these headphones usually cost a bomb due to the technology that they're equipped with, when compared to noise isolating headphones/earphones.

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I hope you all got a clear picture of how these two things work. If you've any doubt/query, drop them in the comments below, i'll definitely get back asap. Do share it with others if you found this to be informative/interesting and be sure to check out other posts here.

Next i will be explaining about the types of headphone amps and i'll also be doing some gear review, so stay tuned!



Reference -

1. ANC

IMPEDANCE IN HEADPHONES - WHAT YOU NEED TO KNOW PT - II

Previously (in part 1), i had explained about the significance of impedance in headphones and it's effect on loudness and quality of the sound delivered, in this part, we'll be going a bit deeper into the following -

1. What is impedance matching ?

2. Significance of impedance matching

3. Sensitivity 

4. When you require an amp

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1. Impedance Matching

It is a process that helps in extracting the best audio quality from a headphone. Each headphone comes with a particular impedance that is used to match with the impedance of the source that you're connecting to.

There exists a rule called "the rule of eighths" which states that the output (source) impedance should be less than 1/8th of the headphone impedance. For example, if someone purchases a headphone with 250 ohms, then the source impedance should be less than 31 ohms. Though decent results can be achieved with slightly greater source impedance, it should be kept in mind that there will be some deviation in the frequency range.

The headphone on the top is the Sennheiser HD 650 which comes with an impedance of 300 ohms and the one below is the Steinberg UR22 MK II which has a phone output impedance of 40 ohms.

So in this case, when we apply the 1/8th rule, the phone output impedance should ideally be 37.5 ohms (300/8=37.5) but as stated earlier you can still get away with a little mismatch with only a slight deviation in the frequency range.

2. Significance of Impedance Matching

For general use/casual listening, an impedance mismatch doesn't really matter much because the differences aren't really noticeable but when it comes to studio application/critical listening, it is very important that there is proper impedance matching else there will be some sort of frequency deviation (i.e. coloration) which will mislead the listener during a mix session etc.

In some cases there will be distortion, especially in the high frequencies and sometimes when you connect a high impedance headphone into a mobile phone or PC, there will be insufficient output volume which can be sorted out by using a suitable amp.

3. Sensitivity

In a nutshell, sensitivity refers to how loud the headphone can get. it also tells us how efficiently the electrical signal gets converted from the source device to an acoustical signal. More the sensitivity, more the loudness and vice versa. Similarly, more sensitivity requires less power while less sensitivity requires more power to obtain substantial loudness.

It should be kept in mind that a headphone with high sensitivity can also produce distortion at very high volume and may even damage the driver. It is advised to stick to a sensitivity rating of 100 dB which is a safe zone in terms of loudness (90dB is on the lower end while 110 dB is on the higher end).

4. When you require an amp

As discussed in part 1, there are 2 types of impedance - high and low. A headphone with an impedance rating of 100 ohms or more requires an amp to achieve substantial loudness. On the other hand, headphones with less than 50 ohms don't require any amplification as they are loud enough by nature.

The Beyerdynamic DT 770 PRO (80 ohms) being connected to the Fiio E11 headphone amp. 80 ohms lies in the grey area which means amplification is not really necessary at all times.

But buying an amp blindly will lead to more complications, so before one can invest in an amp, a ton of research should be done so that it actually compliments the headphone that is going to be plugged into. Factors such as impedance matching, rated sensitivity etc should be kept in mind while investing in an amp.

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Hope you all got an idea of what impedance matching and sensitivity is and the roles that they play in delivering proper sound quality - atleast to some extent. Had to do a ton of digging so that i could put it in the simplest way possible. If you've any queries/feedback do drop them in the comments below, will surely check them out. I will also be coming up with a headphone buying guide that'll help you decide what you want and what you don't want when it comes to headphones. So stay tuned!!



Check out the links below if you want to dive deep into the technical stuff -
1. NwAvGuy
2. Headphones impedance demystified

CABLES - BALANCED & UNBALANCED

From the home theater setup to the recording studios, we've all come across different kinds of cable being put into use, each having a purpose of it's own. In this blog, we're going discuss about the following stuff that one needs to be aware of before setting up their stuff -

1. What are Balanced & Unbalanced cables

2. Difference in terms of their output.

3.  Purpose & usage

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 1.1 Balanced Cable

A balanced cable is the one that has 2 conductors and a ground - total of 3 pins (thus, 3 wires). The 2 conductors carry audio signals which are identical to each other but 180° out of phase which helps in canceling the noise at the receiving end (more on this in section 2). The ground wire acts as a shield against the radio frequency interference that is caused during the transmission.

A typical XLR cable

Examples of a balanced cable includes XLR, TRS etc. They can be quite long (as much as 25-30 meters) without much of any restriction since it is shielded properly.
 
1.2 Unbalanced Cable

An unbalanced is the one that has only 2 wires in it. One conductor and one ground wire, the conductor wire does the job of carrying the audio signal and the ground wire here does the job of shielding as well as carrying a bit of the audio signal (identical to that of the conductor). Thus, the shielding is naturally less effective than a balanced cable.

RCA cable that is used in most AV systems

Examples of  unbalanced cable includes RCA, TS etc. They cannot be longer than 4-5 meters as they tend to pickup a lot of noise along the way.

The TRS and TS cables are the ones that we often use a lot, they look pretty similar yet they are different with respect to their structure and output audio signal. The differences are as discussed below -

2. Difference between balanced and unbalanced cable outputs.

As you can see the one on top happens to be the TRS cable (Tip Ring Slip) while the one that's below is the TS cable (Tip & Sleeve).

The TRS cable has 2 conductors, one which carries a non inverted signal (Hot signal) & the other which carries an inverted signal (Cold signal). The signal that is being transmitted on both the conductors are identical to each other (including the noise) & at the receiving end, the inverted signal is reverted to the original polarity while the noise still remains inverted, which gets cancelled at the receiving end and finally, the original/input audio signal is obtained. 

On the other hand, the TS cable has only one conductor which carries the audio signal and due to this reason, the shielding is also poor which results in interference. Hence, at the receiving end you get a signal that is slightly distorted.

Now that we're done with discussing the differences, let's take a look at when and where they can be used -

3.1 The balanced cables are obviously better than unbalanced ones as they do a better job of removing the noise during the transmission of the audio from one point to another. Hence, it is preferred more than the later.

3.2 The unbalanced cables are preferred in an environment where the length of the cable required is short as longer distance will invite more noise/interference.

It should also be kept in mind that interchanging i.e using balanced cables instead of unbalanced cables (& vice versa) won't be of much use (in fact it may produce below par results). So one should always be aware of the type of connection that is available in the sending/receiving units and use the relevant type of cable connection.

Now that you're aware of balanced and unbalanced cables & it's usage, there's one more thing you should also know about, so hopefully you won't run into such issues while setting up your stuff.

BONUS SECTION!

Instrument cables and Microphone cables are some of the widely used things in a studio/live set up and more often than not, it is used in the wrong manner resulting in poor audio quality etc.

Let's talk about instrument cable first, they're designed to have high impedance and low power. It is usually used to carry a weak signal (for example, a guitar) to the amp. It is a co-axial cable consisting of a central conductor surrounded by a braided shield, this is because the weak signals can easily be distorted by outside RF/electromagnetic waves.

The speaker cable on the other hand is designed to have low impedance and high power. It is used to carry powerful signals from the amp to the speaker. It consists of 2 thick copper wires with no special shielding as it is far less affected by outside interference.

It is not advisable to use an instrument cable instead of a speaker cable because the thin wire in the instrument cable cannot handle the high power that comes out of an amp. It'll naturally generate a lot of heat and in some cases, might even damage the amp/speaker.

If you use a speaker cable in place of an instrument cable, the audio signal will be transmitted but with a lot of electromagnetic interference. Hence one should be aware of what to use and where it should be used.

I hope you found this post to be useful and practical. Do share it with people who might benefit from these tips and if you've enjoyed reading this or have any queries, then do drop them in the comments below, will definitely answer them asap!

Until next time.


References -
1. instrument cables arent the same as speaker cables
2. balanced vs. unabalanced cables

THE DIFFERENT TYPES OF AUDIO COMPRESSION

Before we can get started with compression types, there are 3 aspects that we should understand -

1. Sample rate

2. Bit depth

3. Bit rate

Let's talk about Sample Rate first. The sample rate, is the number of samples per second. It is also referred to as Sample Frequency, higher the sample frequency, the closer it is to the original analog sound. It is usually measured in Hertz (Hz). The most relatable one that we've all come across is the CD which is recorded at 44.1 khz which is twice the amount of human hearing. This is done in order to prevent the loss of data during the sampling process (from analog to digital).

Next comes Bit Depth, which is directly proportional to the dynamic range. It is the number of bits/sample. Higher the bit depth, more is the dynamic range which eventually leads to a better audio quality. The most commonly used ones are the 16bit and 24 bit.

Finally coming to Bit Rate, it is number of bits (data) encoded per second. It basically determines the streaming quality. It ranges from 64-320 kbps for MP3s & goes upto 1411 kbps for WAV format. It is calculated as sample rate * bit depth * no. of channels.

Now that we're done with these 3 aspects, let us take a look at the different types of compression that we generally come across.

There are basically 3 categories -

1. Uncompressed

2. Lossless

3. Lossy

Let's take a dive into each one of these -

1. Uncompressed

The original (digital) data as such is referred to as uncompressed format. They are the most real and raw version of the analog sound signal. Examples of this include WAV & AIFF. Since the files do not undergo any kind of compression, there is no loss of information, which results in the highest quality audio and is of a fairly large size.

Music producers / Mix engineers / Mastering engineers and for other studio related purposes, the WAV format is the benchmark as it doesn't lose it's quality even when there is some editing / changes done to it.

Fig 1 - Spectrum of a .WAV file

2. Lossless Compression

Lossless files are a stripped down version of the uncompressed format. The only difference between this and the uncompressed is that the lossless format occupies lesser space without much loss in quality.

Though it reduces the data in the process of compression, the audio quality remains unaffected. Lossy compression is also called irreversible compression. Examples of this include FLAC & ALAC.

3. Lossy Compression

This type of compression basically reduces all the three aspects of the audio sample. At the same time, some of the information is lost which results in degradation of the audio quality, depending on how much data is lost, the quality also differs.

Fig 2 - Spectrum of a .MP3 format

 From the image you can see that some of the frequencies are cutoff (compared to .WAV spectrum in fig 1), this happens during the compression process. It usually removes the frequencies that are out of the human hearing range (i.e. 20 - 20khz). This helps in reducing the overall file size.

Lossy compression is also called irreversible compression. Advantage of this is that it takes very little space for storage compared to other 2 types of compression. Example of lossy formats include MP3,WMA etc.

Therefore, there is no format which can be completely ignored, they all have their uses depending on the purpose. If you're in a professional environment, then the WAV format would be your go to choice, if you're just going to listen to music & don't mind much about the storage, then your best bet would be FLAC/ALAC and if space happens to be a constraint, then MP3 is the most ideal format. So choose wisely!

I hope you got something out of this and if you have any questions, do drop them in the comments. If you enjoyed reading it, then please do share it. In the upcoming blogs, i'll be reviewing some of the gear that i own, so stay tuned!


References :
Sample rate & Bit Depth
Understanding Audio Quality 1
Understanding Audio Quality 2

TYPES OF HEADPHONES - AN INTRO

Ever wondered why headphones come in various shapes and sizes? Why some cost less while some cost a bomb? Some require an amp while some don't? Well, in this post, i have discussed the different types of headphones from various brands in terms of their pros and cons with their working principle.

Headphones can be classified on the basis of -

I. Earcup Design

II. Connecting Technology

III. Type of Driver used

Let's jump into the details -

I. Based on Earcup Design -

1. Closed back headphones

The Senheiser HD280, as you can see the outer casing is completely closed.

Probably the most commonly seen type of headphones used by people in general. The outer casing is completely closed which means there will be no/minimum sound leakage though it does cause heating up of headphones, making the ears feel uncomfortable after prolonged usage. The noise isolation is also better than open back headphones.

2. Open back headphones

The Beyerdynamic DT990 pro which comes with an open back design, widely used in studios for monitoring purposes.

They're generally used by studio professionals/audiophiles. Regarding the design, the outer casing usually consists of perforations or a mesh type design, which will allow the free flow of air & sound, providing the user a more "wider soundstage" but it also means that there will be some considerable amount of sound leakage due to which people near you can hear what you're listening to.

Bottomline - if you're going to use it in an isolated environment like a studio or inside your home then you can go definitely go for the open back ones.

3. Semi open back headphones
 

The AKG K240

Well, the semi open back headphones as the name suggests has a mixture of properties i.e properties of closed back and open back. They're mostly used for critical listening by studio professionals.

4. Supra-aural headphones

The Grado SR325

These are otherwise known as on ear headphones as they literally sit right on your ears (because the size of the earcups aren't big enough to enclose the ears). They are quite portable as they don't weigh much. The downsides are that, one, since they rest on your ears, after prolonged usage the pressure builds up which leads to some discomfort and two, they don't isolate the ambient noise well enough, this becomes a problem when you're in a public space.

5. Circum-aural Headphones

The Sony MDR7506, with earcups big enough to enclose the ear

They are also called as over ear headphones as the earcups are big enough to enclose the entire ear giving the user a much better sounding experience as they isolate the ambient noise. Nowadays, these type of headphones are the most commonly used type due to its comfort and relatively better noise isolation.

II. Based on connecting technology -

1.Wired

As the term suggests, these type of headphones usually transfer the audio signal via wires that are connected to the source.

2.Wireless/Bluetooth headphones -

These are the type of headphones that make use of the bluetooth technology to transmit the audio signal. A big advantage is that they solve the problem of the wires getting tangled. There are also wireless headphones that don't actually use bluetooth connectivity but they're extremely rare to be found in the consumer segment.

III. Based on the driver technology -

Before we can get started with the different types,

What's a headphone driver ?

It is basically an electromagnetic component which converts the incoming electric signal to a sound signal that is perceivable by the ear. It comes in various sizes & in some cases multiple drivers are used to reproduce the sound more accurately.

Now, let's jump to the different types -

1. Dynamic or Moving Coil

Most headphones use the Dynamic/Moving Coil driver as it is cost effective.

This type of driver is the most commonly used as it is less sophisticated and hence the cost of manufacturing is naturally less compared to other driver technologies.

Working

Consists of 3 parts - A magnet, voice coil & a vibrating diaphragm.The magnet is attached to the frame of the headphone while the voice coil is suspended in the magnetic field of the magnet, which is attached to the diaphragm.

The moment the electric signal flows, the magnet magnetizes the voice coil which in turn creates a magnetic field of its own which causes the diaphragm to vibrate (displacement of air), this process creates the desired sound waves. The bass produced is directly proportional to the amount of air displaced in the process.

The vibrating diaphragm

2. Balanced Armature

The Shure SE846 which comes with 4 drivers to increase the sound quality by assigning certain frequency range to a particular driver.

Balanced Armature drivers are usually found only in IEMs (In-Ear Monitors) due to their small size. It has much better efficiency compared to other drivers on this list.

Working

As seen above, the driver consists of a coil surrounded by magnets on either side. The armature is positioned in such a way that the net pressure exerted on it is zero, hence the term "balanced". When the electric signal passes through through the coil, it magnetizes the armature in such a way that it starts to rotate in one direction thus resulting in the diaphragm to move continuously & produce sound.

3. Planar Magnetic or Orthodynamic Driver

The Audeze LCD-3, the company Audeze specializes in manufacturing planar magnetic headphones.

These type of headphones can get pricey but at the same produces extremely good sound, probably the best due to its unique technology (which is discussed below).

Working

Different sections of planar magnetic headphone. source

Here, a thin diaphragm is sandwiched between two strong magnets instead of a coil like in the case of dynamic driver headphones. The similarity is that both use magnetic fields to produce sound. The diaphragm has wire pattern running over it. When current passes through the wire, it sets up an electromagnetic field which interacts with the existing magnetic field which makes the diaphragm move back & forth which ultimately results in the production of sound waves. When the diaphragm moves back & forth, it has to move uniformly for which the magnet need to be big & efficient, due to this the headphone naturally becomes heavy and in most cases require an amp.


4. Electrostatic Driver

The Stax LR-300 with an amp

This category of headphones are probably the most expensive among the entire list. Naturally, they aren't seen as often as the other types in the market.

Working

Here there is no magnet involved in the reproduction of sound from the electric signal. Instead, it uses the principles of static electricity. It consists of a thin diaphragm suspended in between two stators. When the current is passed to the stators there is an alternate current polarity which is induced into them. This varying polarity causes the diaphragm to move back & forth forcing the air to be displaced through the perforations & this continuous displacement of air due to the varying electric field is what causes the sound to be produced.

5. Magnetostriction or Bone Conduction

Bone conduction headphones by Aftershokz

It is the result of technological surge that has occurred in the recent past. In this type, there is no direct contact with the ears instead the sound waves are conducted by bones i.e the bones present in the skull. The driver basically converts the sound signal by sending in the vibrations. Though this type of driver isn't as good as other drivers of in terms sound quality, it is very helpful for the people who are deaf / have hearing loss as it lacks the role of eardrums in the process.


Hope this was helpful & informative to the readers. In my upcoming blogs i'll be talking not only about audio tech but also about electronic music, so stay tuned!

Sources -
Types of drivers

Planar magnetic tech

IMPEDANCE IN HEADPHONES - WHAT YOU NEED TO KNOW

What is impedance ? (in headphones)   

• In layman terms, it is the resistance that the headphone offers. It is measured in Ohms (Ω). 
• With the increase in impedance, the power that is required to drive the circuit also increases.

 

The beyerdyamic DT 770 pro (250 ohms version). It also offers the 32Ω & 80Ω for consumer level application.

Types of impedance :

Low impedance 

• Headphones that have an impedance rating of less than 50 ohms are considered to be low impedance as they can be driven by any consumer level device like a laptop, mobile phone etc. 
•  They don't require a dedicated amp.

High impedance 

• Headphones that have an impedance rating of over 100 ohms are generally considered to be high impedance as they require a dedicated amp to obtain normal hearing volume.

Impact on loudness :

• Normally, headphones with a lower impedance rating sound loud enough whereas headphones with a higher impedance can also deliver enough volume provided it is complimented by a suitable amp.
• If the headphones are going to be connected to a laptop or a mobile phone etc. , then one can go for the lower impedance headphones as they require lower power whereas if the headphones are to be used for mixing/studio related purposes then, ideally, one can go for higher impedance headphones with an amp.

Impact on sound quality :

• As such it doesn't really affect the sound quality but a higher impedance rating does help in reducing the distortion that occurs in the background. Here's how - 
• The impedance depends on the kind of winding that the voice coil has got. A headphone with higher impedance rating will have very thin wires running around the coil which reduces the air gap and this in turn increases the strength of the electromagnetic field which finally reduces the distortion that occurs in the background as compared to headphones with a lower impedance rating.

If you want to know more about impedance and stuff, check out the links below -

1. NwAvGuy

2. CNET- low vs. high impedance 

In my upcoming posts, i'll be explaining about stuff like factors affecting headphone quality, things to keep in mind before purchasing headphone, gear reviews etc. 

So stay tuned!