Introduction to Technology, Communications And Media

Signal Processing Equipment

There are different types of equipment that is most commonly used to send and receive signals i.e. microphones and CD players, amplifiers, and speakers. Another name given to this equipment is signal processing equipment. These also include:-

• Equalizers
• Compressors
• Limiters
• Noise Gates
• Effects processors

Signal processing equipment is normally used with auxiliary inputs linking to the sound board or is inserted in to each channel. Some sound boards enable users to connect an insert cable in to either the input or output channel. This cable enables the signal to pass through an external piece of equipment before entering the sound board by interrupting the signal path. I.e. if a sound effects processor is plugged in between the CD player and the Amplifier then the sound will travel through the sound effects processor which adds the sound effect before sending the audio signal to the amplifier which in turn sends it out through the speakers.

Sound Equalizers

The band will require an audio processing unit also known as EQ. The process used to change the frequency of sound by passing it through a channel, it basically means to correct, equalise the frequency response of a signal. Equalizer is commonly applied as a general term for audio filters by mistake. Most of the DJ mixing equipment and hi-fi audio components which are available these days often include graphic equalizers or simply equalizer. These are actually all purpose filters which can be arranged to produce the effect of band pass, high pass, low pass and band stop filters. The band will require this equipment to help make the sound clearer.

Compressors / Limiters

By using compressors or limiters the band will be able to avoid problems such as volume not loud enough or be too loud at times. A compressor/limiter helps reduce the dynamic range of an audio signal simply by making quieter things louder vice versa. Different controls are available such as attack and release times, threshold levels, and compression ratios.

Noise Gates

While the band records the music cd they will need to avoid unwanted noise for example when the microphones pick up unwanted background noise, like cheaper computer sound cards give out a lot of hiss that is especially noticeable when the sound system is usually quiet. Microphones may pick up background noise that could be distracting when played through a bigger sound system. These problems can be mostly eliminated by using devices known as noise gates. A noise gate will not let an audio signal pass through it unless it is above the threshold level which is set by a knob on the front of the equipment.

Effects processors

Audio special effects such as pitch shifting, reverberation, and delay are often desirable in a theatre application. Effects processors also known as multi-effects units enable a number of audio effects to be in one box. There are not any standard types of effects processors but each has different number of effects, different sound quality, and different user interfaces. Some commonly:

• Delay - This delays the audio signal for a certain period of time before it is played, i.e. few milliseconds to a few seconds are most common. Echo effects are commonly done with delays.
• Reverb - Reverb effects replicate room characteristics and can usually be changed to simulate different types of rooms and room sizes and.
• Flanging and Phasing - Two effects that are mostly used by everyone, both flanging and phasing can make the sound appear to ``swish and swoosh''.
• Pitch Shifting - Most pitch shifters either increase or decrease the pitch of the sound. Making it higher frequency or lower frequency.

Digital and Analogue Recording Techniques

There are two types of recording music that the band will have to consider, Analogue recording which basically records onto a magnetic tape. Digital recording however the music is recorded onto either CD’s, hard drives which are a part of a computer or a standalone digital recorder also it can be digital information recorded onto a tape i.e. Alesis ADAT, Tascam D88 etc.

Analogue recorded tapes have a sound which digital recording attempts to emulate a lot of the time. Digital hard drive recording that pretty much has taken over the digital tape domain, and gives you more opportunities to manipulate parts of the music i.e. takes, fixes etc. Most of the digital recording equipment, software, and plug-ins emulate analogue recording equipment for example tape, solid state & valve/tube outboard units this is because it is a sound that 'listeners' are used to i.e. warm, soft, friendly etc. Analogue recorders and outboard will never emulate a digital sound because it doesn't have the capacity to do so even if anyone wanted to do it.

Digital Recording

Digital audio works by converting sound into binary coding in a bid to save space to make things easier for everyone the sound is encoded into 16-bit PCM (pulse code modulation) and usually sampled at 44,100Hz. This configuration is usually for CD’s (compact discs). First the sound is sampled by using PAM (pulse amplitude modulation). The sampled amplitude of waveform is measured by each sample taken.

The analogue signal which is transmitted from the input device to a device called analogue to digital converter (ADC). This in turn converts this signal to a series of binary numbers. The count of the numbers created per second is called the sample rate. A bunch of wires transmits these numbers into storage i.e. hard drive or CD using a compact disc burner which are widely and cheaply available.

Analogue Recording

Analogue audio recording when music is recorded on a magnetic tape, the process converts sound into a voltage and polarises the magnetic particles in a way which is more or less analogous to the sound produced which basically means the sound’s sampled instantly at a considerably faster sampling rate.

As our band wants to create and distribute music on CD’s the preferred method of recording music for the band will be digital Recording this is because unlike analogue recording digital recording eliminated the hissing sound which are present with analogue recording, also the music will directly be saved on to the hard drive there for making it easier to transfer it to a compact disk as required by the band.

Correcting or enhancing signals

The main advantages of digital recording over analogue recording are its ability to correct errors. Since these bits are actually extremely small, some are inevitably damaged during the recording process. With analogue recording any damage that is caused can not be reversed. Over a period of time the noise gets worse and worse.

Sampling Rates

Sampling Rates

The analogue signal is ‘sampled’ over a certain period of time for example say 1sec the result is the analogue signal is sliced in to segments, more segments that there are within the time period results in a more precise representation of the analogue signal. Once the signal has been digitized it can be manipulated in many different ways i.e. effects such as Reverb and Echo can be added, pitch can be altered, and finally the speed can also be altered.

Sampling rate also affects the recording quality meaning the higher the sampling rate the better the dynamic range of the recording. However if the sampling rate turns out to be too low it will intercept a waveform too few times to make a proper analysis of the sound. Therefore the sample will not intercept the signal enough times to build a precise representation of the sound recorded.

The frequency response of an average human ear is around 20 - 20,000Hz therefore ideally the sampling rate must be at least double the upper value which then allows it to capture and analyse the full human audible range. 8-bit sound sampled at 22,000Hz normally used in computer games and the web this is because of space constrictions. A sampling rate of 200,000Hz and an encryption of 96-bit would be good, but there isn’t a computer powerful or big enough to record a sound at that level.

How to make a music CD

There are many different hardware components and software’s on the market which can be useful to our band to enable them to create a cd, firstly they will require a cd burner which can be of various different read and write speeds ranging from 28x to 56x. CD burners work by a laser beam that is used to read and write binary code off of the reflective surface of the disc the laser also is used to read the binary code of the surface and convert it back into the original form and is played back.

The band will also require software to burn music CD’s there is a wide variety of burning software which is on the internet for example Nero Burning Rom, Roxio CD Creator, Acoustica MP3 CD Burner and many more. These software will help the band to create a number of CD’s.

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