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Digital vs. Analogue
Digital vs. Analogue
Sound can be recorded in either an analogue or a digital format. Digital recording only became a possibility in the 1980’s, so up until then, everything was recorded in an analogue format.
The edexcel definition of analogue is “when a signal or equipment uses a continuously variable physical quantity.” What this really means is that an analog audio signal is an exact copy of an original audio signal, whereas a digital signal represents this original signal in terms of digits or numbers.
Signal to Noise Ratio
Signal to Noise Ratio
Signal-to-noise ratio is “the difference between the audio that is being captured and the noise being captured simultaneously.” You want to maximise the signal-to-noise ratio so that there is more signal than there is noise in your recordings. There is more information here on how to do this.
In terms of how signal-to-noise ratio is affected by analogue and digital equipment, analogue recordings generally have a lower signal-to-noise ratio than digital recordings - that is to say that there is more noise on analogue recordings and have narrower dynamic ranges. Recording to analogue tape adds hiss to the signal, as does playback on vinyl and cassette. Noise is also added when signal is processed through analogue hardware, such as effects units.
Frequency Response
Frequency Response
Frequency response is the ability of a device to process and/or produce the range of frequencies perceptible by the human ear. Analogue audio has a better frequency response than digital audio does. This is because the frequency response of a digital signal is 'hard coded' by the sample rate used (see Nyquist's Theorem below), but analogue audio is theoretically infinite.
The frequency response of analogue recordings are limited by the recording and playback equipment. For example, recording to wider tape allows for a higher frequency resolution than thinner tape does. The highest quality tape machines have been known to record frequencies up to 200kHz (considerably higher than human hearing). In terms of playback format, vinyl has a frequency response from 7Hz to 50kHz, where as cassette can only reproduce frequencies of up to 20Hz, or 15Hz if the signal is at a higher level (dB).
Headroom
Headroom
"Headroom is the ratio of the maximum amount of undistorted signal a system can handle compared to the average level for which the system is designed. For example, suppose you have a home recording setup with a nominal -10dB average level. If you can pump out +8dB signal through your system without distortion, then you have 18dB of headroom." - Sweetwater, Craig Anderton
Analogue has better headroom than digital.
Clipping
Clipping
Clipping is the overloading of a signal, so that the top of the waveform becomes squared or is cut off. It can lead to your audio sounding distorted.
Digital clipping is known as hard clipping and analogue clipping is known as soft clipping.
Valve vs Solid-State Amplifiers
Valve vs Solid-State Amplifiers
Valve Amplifiers
Valve Amplifiers
Valve amplifiers were the first type of amplifier to be invented and used. They were invented in 1906 by Lee De Forest, but weren’t used to amplify the instruments with pickups until the 1930s. They fell out of use once the solid-state amplifier became commercially available in the late 60s/early 70s. However, there has been a resurgence in the use of valve amplifiers in recent years.
The guitar amps that you’ve probably seen have a pre-amp, a power amplifier and a speaker all contained within a case or cabinet. Despite the fact that there more than just an amplifier in there, they are still simply referred to as amps (or amplifiers). Each amplifier (pre-amp and power-amp) uses either one or two glass valves each to boost the signal. In order for the amp to work, the valves have to get warm.
Solid-state Amplifiers
Solid-state Amplifiers
Solid-state, or transistor amplifiers, came into use in the late 60s/early 70s, despite the fact that they had been designed in the 1940s.
As the name suggests, this type of amplifier have transistors inside, instead of tubes or valves, to amplify the sound. A transistor is “an electrical semiconductor that is used for switching or amplification.” Similar to the valve amplifier, the signal passes through a pre-amp and a power amp in order for the speaker to produce sound.
Analogue to Digital Conversion
Analogue to Digital Conversion
Converting a signal from analogue to digital occurs at the point in your signal chain when the analogue signal from your microphone needs to be read by your computer digitally. A/D converters are (usually) featured within your audio interface.
As explained above, a digital signal represents an analogue signal in terms of digits and/or numbers. An A/D converter works with sample rate and bit depth.
Sample rate takes little “snapshots” of the analogue signal, and controls frequency resolution. It's sort of similar to how you film something – your camera shoots in frames per second and combines all of these frames to make a moving image.
The standard sample rate is 44,100Hz, meaning that 44,100 samples are taken each second. This is commonly expressed as 44.1kHz. The reason for this sample rate being the standard is because of Nyquist’s Theorem.
Nyquist’s theorem states that to fully recreate an analogue signal digitally, the sample rate must be at least twice the highest frequency in the signal. Human hearing ranges from 20Hz to 20,000 Hz, and 20,000 doubled is 40,000. In 44.1kHz sample rate, the extra 4.1Hz is just for safety. The reason why it must be double the highest frequency is to ensure that all the peaks and troughs in the waveform are accounted for.
Bit depth is the resolution of amplitude, as opposed to frequency. The more bits of information you have, the larger the dynamic range. The standard bit depth is for CDs is 16bit and for most streaming services, it is 24bit.
Streaming Bit Rate
Streaming Bit Rate
Bit rate is how many thousands of bytes (kilobits) of information are stored per second of audio. Bit rate refers to the playback resolution of an audio file, not to be confused with sample rate and bit depth which refers to the resolution at which audio is captured.
The more kilobits there are per second (kbps), the higher the sound quality. Sound files with lower bitrate will have been compressed more than a file with a higher bitrate.
Which bit rate you choose depends on the application (streaming services want lower bit rates so transmission rates are quicker) and not all consumer formats have a set bit rate so there are always a few you can choose from.
Digital to Analogue Conversion
Digital to Analogue Conversion
Digital to analogue conversion is the exact opposite process to analogue to digital conversion. A DAC (digital to analogue converter) inputs a binary number and outputs an analog voltage or current signal.
Compressed and Uncompressed Digital Formats
Compressed and Uncompressed Digital Formats
Digital consumer formats are either uncompressed or compressed.
Uncompressed audio files are the best quality because they are perfect representations of the audio recorded, but it results in a large file size. FLAC is a lossless format, meaning that the quality isn’t affected at all.
Compressed files are of lesser quality because in order to compress the file some data has to be discarded, but on the other hand the file size is considerably smaller. Compressed digital formats became popular in the late 1990s because, unlike uncompressed digital formats, they were small enough to be transferred over the internet and be stored on a playback device such as an iPod.Compressed files can either be lossy or lossless. Lossy compressed files lose some audio quality in the compressing process but lossless compressed files don't lose any quality.
The most well known compressed digital format is the mp3 file, which is a lossy format, meaning that some audio data is lost when it is encoded. MP4 is a format that is primarily used by iTunes and it is also a lossy format but, the quality degradation isn’t quite as obvious.
You can determine the degree to which a compressed file has been compressed by looking at the bit rate (not the bit depth). The bit rate is how many kilobytes of information there are per second of audio. The more kilobytes there are per second, the higher the sound quality, but the less compressed the file is.
CDs, which use uncompressed file formats such as wav, can have a bit rate of up to 1,411kbps (kilobytes per second). In comparison, mp3 files have bit rates of between 96kbps and 320kbps, showing how much the audio is compressed.
Compressed digital formats are used in two ways; for downloading and for streaming. The downloading process is a one time thing whereby you pay for the music and then it is kept, much like an online store. Streaming, however, allows you to listen to whatever you want with a subscription fee, without having to buy the music or own it.
Advantages of Compressed Digital Formats
Advantages of Compressed Digital Formats
Don’t suffer from degradation.
Very easily portable (iPods and phones are pretty small)
Streaming can be a cheaper to listen to music as you don’t have to buy the music.
You can get lossless compressed digital formats which are just as good as CD quality.
Compressed digital formats don’t take up a lot of space on devices compared to uncompressed formats.
Music/audio files can be more easily shared.
Problems with Compressed Audio Formats
Problems with Compressed Audio Formats
Lossy compressed files are of lesser quality than uncompressed formats; "detail associated with frequency and dynamics is lost through this process."
Artists receive less money from streaming services than they do through downloading or CD sales.
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