Soundware Guide to Basic Digital Audio

Soundware Beginners Guide to......Basic Digital AudioTo produce high-quality recordings on your computer, it helps to know a little about the theory of sound and how it relates to digital audio.Comments/suggestions for our beginners section? Contact us!Sound BasicsSound into electricity (analogue audio)Analogue to digital conversionResolution, sample rates and sound qualityDigital audio formatsAdvantages of digital audio Sound BasicsSound is transmitted through the air as waves of high and low air pressure created by a vibrating object such as a guitar string. The number of vibrations per second is known as the frequency of a sound low frequency sounds sound low pitched to us, whereas higher frequencies are heard as higher pitches. Frequency is measured in kHz, and the accepted range of human hearing is of frequencies between 20kHz and 20,000 kHz between twenty thousand and twenty million vibrations per second (although this decreases, particularly at the high-frequency end, with age or owing to damage caused by excessive loud noise).Sound into electricity (Analogue Audio)To record audio, the sound first needs to be converted into an electrical signal. The process by which this is achieved takes advantage of the motor effect the fact that when an electric current is run through a magnetic field, a force is created. So, if a magnet is suspended within a wire coil and a current is run through the coil, the magnet will move (or, if the magnet is fixed, the force will be transferred and the coil will move instead). Conversely, therefore, if a magnet is moved within a wire coil the opposite will occur an electrical current will be generated in the wire.So, to make a simple microphone, a wire coil is attached to a diaphragm (a flat piece of material that will vibrate like a drum skin) and a magnet is fixed within the coil. When sound waves hit the diaphragm it vibrates, and the spring moves at the same frequency as the sound waves. Since it is moving within the magnetic field created by the magnet, an alternating electrical current is created that is proportional to the frequency of the sound vibration that hit the diaphragm.A simple moving-coil microphone.To make a speaker, the process is reversed the electrical current from the microphone is passed through another coil, again attached to a diaphragm and with a magnet fixed within the coil. The current in the coil within the magnetic field causes the coil to move, which causes the diaphragm to move again at the same frequency as the original sound vibrations that caused the microphone diaphragm to move. As the diaphragm moves, it will cause the air around it to vibrate as well, and will transmit sound waves identical (in a perfect world in reality there is always a certain amount of electrical interference, resistance etc. which affects the resulting sound) to the original sound waves.A simple loudspeaker.This is the principle of all analogue audio recording equipment and is the basic design upon which all microphones and speakers are modelled.Analogue to Digital ConversionAnalogue audio works according to variations in an alternating electrical current. The differing voltages and the alternation of the current corresponds exactly to the original sound wave (the word analogue comes from the same root as analogy and analogous referring to things that relate exactly to something else). However, digital technology works on completely different principles data is converted into binary code made up of ones and zeroes. The analogue medium can express infinite variation in signal levels, whereas digital technology works on an on/off principle by its very nature (think of a digital watch with changing numbers compared to an analogue clock face with gradually moving hands.) So, to convert analogue audio into a digital format it must be converted into binary code that can be read by a computer.To do this, the electrical current that represents a sound is passed through an analogue-to-digital converter. This takes readings of the voltage of the current many thousands of times per second, which it then rounds to a whole number and converts into a binary value. Conversely, a digital-to-analogue converter reads the code and converts each of the binary values to an electrical pulse that makes up a current very similar to the original analogue signal. These two converters are usually combined into one AD-DA (analogue-digital, digital-analogue) converter.Resolution, sample rates and sound qualitySample RatesTo convert an analogue signal into a digital format, it is passed through an analogue-to-digital converter. This takes readings or samples from the electrical signal many thousands of times a second and converts the readings into binary code. So, the higher the number of samples taken (the sample rate), the more accurate a representation of the original analogue source is delivered and the higher the sound quality. The standard sample rate for CD-quality audio is 44,100 samples per second, which is written as 44.1kHz. The majority of professional digital audio devices operate at 96kHz or higher.Low Sample RateAt low sample rates, the gaps between each reading of the current are large, and the wave is not converted very accurately, resulting in lower sound quality.High Sample RateAt high sample rates, the gaps between each reading of the current are small, so a more accurate representation of the wave is produced, resulting in higher sound quality.

Resolution

The resolution of a digital signal is the range of numbers that can be assigned to each sample. When the sound is passed through an A-D converter, the values that are sampled are rounded to a binary value. So, the greater the number of decimal points the number can be rounded to, the more accurate a representation of the actual reading it gives and the higher the sound quality will be. The number of binary values assigned to each sample is measured in bits (CD quality is 16-bit, and most professional audio devices operate at 24-bits or higher). Low bit rates can cause quantization distortion, where the sampled values are rounded up so much that they no longer give an accurate representation of the sound, and the digital audio signal takes on a crackly, metallic quality. Higher bit rates are also capable of transmitting a higher dynamic range, resulting in deeper bass and clearer high frequencies.Low ResolutionAt a low resolution, the readings are heavily rounded, giving an inaccurate representation of the wave and a lower sound quality.High ResolutionAt a higher resolution, the readings are rounded less and give a more accurate representation of the wave, resulting in a higher sound quality.Digital Audio FormatsDigital audio can be stored in many different formats. In professional audio work, uncompressed audio file formats are used as these generally give the best sound quality. Some examples of uncompressed formats are:AU: A file format (abbreviation for "audio") that originated on the Sun and NeXT computer systems. Not widely used today.Audio Interchange Format (AIF, AIFF): File format for Macintosh system sounds, similar to Windows' WAV format.Compact Disc Digital Audio (CDA): This is format used for encoding music on all commercial compact discs.SND: Another file format (abbreviation for "sound") similar to the AU format and used primarily for Macintosh system sounds.Waveform Sound Files (WAV): This format (pronounced "wave") produces an exact copy of the original recording, with zero compression.A problem with uncompressed digital audio is that the file sizes can be very large, however. To combat this, a variety of compressed audio formats exist that are mostly used to transfer audio over the Internet. These use codecs (short for compression/decompression). A codec converts an uncompressed digital audio file into a smaller format, and will also decode the compressed file enabling it to be played back. Some codecs work by physically removing data from an uncompressed audio file to make it smaller. In this case the file cannot be converted back into an uncompressed format from the compressed file. This is known as a lossy compression method. Others allow the original uncompressed file to be retrieved from the compressed file these are known as lossless compression methods. Lossless compressed files are generally larger than lossy ones, though.Advantages of Digital AudioThe debate over whether digital or analogue audio technology sounds better is long running and will doubtless continue for years to come. In truth, the difference in sound quality between top-of-the-range digital and top-of-the-range analogue equipment is almost indistinguishable. However, for the home user, digital technology has a number of benefits over analogue:Value for moneyDigital technology has made home recording accessible to a much wider audience. Computer multitracking software has in many cases removed the need for hardware mixing consoles and effects, and as such allows a basic recording setup to be much cheaper and more compact. In particular, software emulations of analogue hardware (such as vintage synths) are considerably cheaper than the real thing!Noise resistanceDigital recording is immune to much of the electromagnetic interference that causes noise on analogue recordings. This makes it much more suitable for home recording, as often home studios operate in less-than-ideal surroundings without any of the expensive electrical isolation and shielding of professional analogue studios.CopyabilityDigital audio can be copied infinitely without any loss of quality, unlike analogue audio, which loses quality with each reproduction.DurabilityDigital media such as CDs are much more durable than their analogue counterparts.

Foreign buyer scams US,Nigeria,Canada

most sellers dont have trouble with scammers but there are a few that do , i have made this guide in the hope that you wont get caught out by them!

remember they dont have to live abroad ! ive had a few that were member in the UK but there address and telephone numbers didnt check out

these scammers usually target high priced items like mobile phones,computers or consumer electronics,they usually head straight for new sellers with buy it now products and can cause a real nusance with having to relist and getting your fees back

there are ways to protect yourself from them as follows:-

when you set up your seller account you have options to restrict the type of buyers you dont want such as overseas , bidders with low zero or negative feedback.restrict it to paypal payment only... there are lots of options.

watch your item close to the end of its listing and if any slip through remove there bid fast !

always check these bidders out , look for patterns in there feedback, some will setup spoof accounts selling to themself in order to raise there feedback score, these items will be of very low buy it now items and will sell maybe up to 100 items across anything upto 10 buyer accounts, always checkthere ID history , how long they have been a member, location in the UK , you can check there postcode against multimap or royal mail postcode listings , you could go to the extreme and use the electoral roll to check that they are who they say they are.

i dont need to tell you that you should never send goods out without payment or accept western union mony tranfer, they even have the front to say things like can i trust you ! and i am sendingpayment with my agent fees whichi am trusting you with wanting you to senditon to them asap whichmeans you could not only lose the item , money and postage costs but you actuallywrite them a cheque for there agent fees,

some will offer to pay any amount of postage to get it overseas or make a promise that you can share in the resale profits if you send it now.

save all comunication between you and them , never comunicate through private email some have email addresses at freemail.com always report it to ebay asap so there account is suspended and ebay will refundfinal value fees.

i hope this is helpfull to you and your ebay experience is a good one

Free Subtitle Offers

I recently opened a little e-bay shop and started to fill it with items. I took advantage of a listing offer of free subtitles and listed in excess of 100 shop inventory items with a subtitle. At the end of each listing I was told how much I would be charged 0.08p every 30 days.

When my next fees invoice arrived I was absolutely horrified at the amount and upon closer inspection realised that I had been charge 0.35p for each of my listings that had a subtitle! Obviously there were quite a few of them. There was no mention of this in the small print, no mention of this whilst I was busy filling up my shop. No warning that the offer was about to expire.

E-bay told me that it's policy was to not refund fees! The only advice other than that was that I should remove my subtitles by revising the items if I did not want to be charged for them, they even told me how I could do this. Fine, have you tried to remove a subtitle from an active inventory listing? You are physically unable to, you get an error message and cannot continue.I pointed this out to e-bay and now they say, that is correct I am unable to remove my subtitle by revising the item, I should have to end the listing and then relist it! Great, so not only do I have to spend a day ending all my listings and then relisting them (losing any credit in the meantime for items that would have sold), but stupidly, I cannot do a bulk edit, I have to do each item individually. Thank goodness I'm not a power seller listing 500 items or so!

Anyway, the worst thing about all this mess is that according to the help pages, a subtitle is an enhancement and according to their revision limitations chart for store inventory listings, enhancements can be added or removed any time the listing is active. That is in black

Europa Trading-Amazing value

I would just like to say how much I appreciate Europa International and the excellent service they provided. I recently purchased 2 bikes, the x-dirt 125 Max

Micro bite alarms

They need simply to be attached to your fishing rod just between the reel and the first eye of the same rod. these devices alert you when there is a simple moviment of your line. Worth to get one, very useful when fishing with more than one rod.

Super sensitive to bites

Easily attaches to most rods

Audio alarm

Bright light led

Low power required.

VW 72 Bus

Don't buy one unless you are a glutten for punishment. Although VW made argueably the best bus in 71; they messed everything up in 72. Dual carbs that have flakey linkage , lots of one year only stuff, (including the motor!) and an oil bath air cleaner that is practically impossible to take out without dumping oil all over the moter (no inspection hole), lousy verneer in the Westies. They fixed alot in 73, but didn't really get it right again till 78 with the advent of the 2 litre motor. Just my opinion.

Buying and Selling Amateur Radio Equipment on Ebay

Having bought and sold a fair amount amateur radio equipment on Ebay I felt I could add to some of the excellent information already out there. I lot of what I am about to detail is really a general guide to Ebay.

First of all who sells on Ebay:

Dealers
Licenced Radio Amateurs.
Others
Dishonest people

Dealers

Most of the main ham suppliers use Ebay to advertise special offers, clearance items and used goods. Absolutely nothing wrong with this, in fact, as a new Ebay purchaser this isa good place to start. Just make sure they are who they say they are - there Ebay rating is normally proof enough.

There are some small dealers that trade in components etc. The money involved in these purchases are so low that I would tend to take a risk even if the amount of feedback is low.

Licenced Radio Amateurs

Most are honest. They are normally easy to trace via the RSGB Year book or qrz.com however make sure that you are dealing with the real person. It has been known for a dishonest person to register on Ebay using a bogus call sign as their id. If there is little feedback and the item is expensive try contacting another amateur local to the seller and see if it really is the ham that is selling the rig or whatever.

Others

Remember that the vast majority of Ebay transactions go through without problem. If the item is expensive and there is little or there is high bad feedback then treat with caution (others will). If you can collect the equipment then you may get youself a bargain as others will not bid.

Dishonest People

Look for things that don't stack up. Somebody selling their transceiever will know a lot about it - check they are licensed ask them a technical question or two (if you don't know what to ask seek help fom another ham - most are very helpful).

New Sellers

Ebay is an excellent place to sell ham gear - your get an international audience for your sale. If possible start selling cheap items - buyers are more likely to take a risk with somebody with little or no feedback when the item is cheap. If you are licensed make sure that this is known and give it to any potential buyer. Describe the item honestly - photograph any cosmetic damage if you are claiming the goods to be in good condition. If you are auctioning a transceiver or other expensive item invite potential buyers to inspect the goods.

General

Before bidding on an expensive item find out about it. Let us take the classic FT-101 rig for example. This is an excellent rig and still reaches good prices on the seconhand-market. Searching the Internet you will find out that its mains transformer is a source of trouble if the rig has been over run.One of themain reasons for this is operators running too much power on AM.Before buying one of these I would check to see how long the current owner had used the rig for and make sure that he/she had not used it for AM or that they fully understood the issues.

Some time ago I decided to buy a Yaesu FT1000MP V Field. I checked the dealer prices and the Ebay market. What I realised was that the prices on the USA Ebay were considerably lower than the UK Ebay for this particular machine. I knew that new rigs were less expensive in the USA that in the UK however this did not explain the size of the difference. Checking the USA dealers I realised that Yaesu had dramatically dropped the USA new price. I guessed, as it turns out correctly, that Yaesu were about to replace the FT1000 as the flag-ship. I further realised that the price diffrence was so large that I could save money even if I ended up paying VAT on the import. I found a suitable machine that had a buy-it-now price. The seller had excellent feedback. He had given his call sign so I was able to check him out and found contest logs showing that he was using an FT1000. I asked the seller a few more questions, he answered honestly telling me a lot about the rig and his attitude made me feel comfortable. The whole transaction went without a hitch except that I got stung for the duty and VAT however I still made a considerable saving over the UK prices (they tumbled a few months later when Yaesu dropped the UK prices).

A much cheaper purchase was a FT209. This was described as in good condition. For a machine of this age I would expect some cosmetic damage but it to be fully functional. Although he had little feedbackthe price I paid was very much lower than I had expected When it arrived it was cosmetically reasonable however the memory functions were faulty as was the tone generator plus the display lamp was blown. The lamp and memory were not important but I wanted to use this for mobile so the tone was. An hour or so with the soldering iron plus a couple of minature LEDs and a couple of switches cured all the faults. The reality of the situation was that it was highly unlikely that a rig of this age had no faults so I did not believe his claims. I set my maximum bid price to what I would have expected to pay for a scrap machine. Had he been honest about the condition then I (and others) would have beleived him and placed higher bids.

Constructors

Ebay is a great source for components both current and obsolete. Most of the components that I have purchased have turned out to be very good however I did receive some LEDs from one supplier that were obviously seconds.

Conclusion

With big purchases - use your head not your heart. Check out the seller, check out what the item is really worth and stick to your maximum bid. If you don't win this one then the chances are that another one will turn up again in the following days or weeks. For cheap items - most Ebayers value their feedback rating more than the money made off these, so why not take the risk?