Dynamic Range

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Dynamic Range

• Advanced Lecture

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• dynamic range The ratio of the loudest
  (undistorted) signal to that of the quietest
  (discernible) signal in a unit or system as
  expressed in decibels (dB).
• Dynamic range is another way of stating the
  maximum S/N ratio.
• With reference to signal processing equipment,
  the maximum output signal is restricted by the
  size of the power supplies, i.e., it cannot swing
  more voltage than is available.
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• While the NOISE FLOOR of the unit determines the
  minimum output signal. SMALLEST POSSIBLE LEVEL
• Professional-grade analog signal processing
  equipment can output maximum levels of 26 dBu,
  with the best noise floors being down around -94
  dBu.
• This gives a maximum dynamic range of 120 dB
  almost the range of HUMAN HEARING!

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dBFS

• dBFS means "decibels relative to full scale".
• It is an abbreviation for decibel amplitude
  levels in digital systems which have a maximum
  available peak level like PCM encoding.

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Meterering

• VU Reference Level An analog representation of
  digital signal
• (Standard setting would be "20 Ref" resulting in
  a -20dB FS 0 VU)
• VU Graphic Bar Level Meter Indicates VU level of
  left and right digital audio.

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More on Metering

• VU Numeric Level Meter Indicates VU level of
  left and right digital audio.
• Peak Program Meter Area above the main bar
  indicating peak program levels.
• Maximum Peak Level Meter Displays maximum or
  peak level of the audio program material.

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• VU meters are designed to represent the perceived
  loudness of a passage of music, measuring in
  volume units.
• The product is designed so that the best signal
  quality is obtained when the meter rarely goes
  above nominal.
• The markings are often in dB instead of "VU", and
  the reference level is defined in the product's
  manual.

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• In professional recording and sound reinforcement
  gear, the nominal level is 0 VU 4 dBu.
• In consumer level equipment, the nominal level
  varies, but some standardize to 0 VU -10 dBV.

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Consumer vs. Pro

• The difference between consumer and pro equipment
  revolves around the cost required to create
  larger power supplies and output higher levels
• consumer levels can be generated by
  battery-powered gear, but pro levels require
  power supplies

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Nominal Level

• Nominal level is the operating level at which an
  electronic signal processing device is designed
  to operate.
• Electronic circuits are limited in the maximum
  signal they can output and the electronic noise
  they add to the signal.
• The difference between the internal noise and the
  maximum output level is the device's DYNAMIC
  RANGE.

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More on Nominal Level

• When a signal is chained improperly through many
  devices, the dynamic range of the signal is
  reduced. The nominal level is the level that
  these devices were designed to operate at, for
  BEST dynamic range.
• In audio, a related measurement, signal-to-noise
  ratio, is usually defined as the difference
  between the nominal level and the noise floor,
  leaving the headroom as the difference between
  nominal and maximum output.

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• It is important to realize that the measured
  level is a time average, meaning that the peaks
  of audio signals regularly exceed the measured
  average level.
• The headroom measurement defines how far the peak
  levels can stray from the nominal measured level
  before clipping.
• The difference between the peaks and the average
  for a given signal is the crest factor.

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• The crest factor or peak-to-average ratio (PAR)
  or peak-to-average power ratio (PAPR) is a
  measurement of a waveform, calculated from the
  peak amplitude of the waveform divided by the RMS
  value of the waveform.

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• 0 dBFS is assigned to the maximum possible level
  in a digital signal A signal that reaches 50
  of the maximum level would peak at -6 dBFS, for
  instance.
• All peak measurements will be negative numbers.
  There are NO Positive Numbers

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• Dynamic Range Comparison
• AM Radio 20-30 dB
• FM Radio 40-50 dB
• Vinyl microgroove phonograph records typically
  yield 55-65 dB, though the first play of the
  higher-fidelity outer rings can achieve a dynamic
  range of 70 dB.

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• A dynamic microphone has up to 140 dB dynamic
  range, while condenser microphones are limited by
  the overloading of their associated electronic
  circuitry.
• Practical considerations of acceptable distortion
  levels in microphones combined with typical
  practices in a recording studio result in a
  useful operating range of 125 dB.

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• Compact Cassette tape performance ranges from 50
  to 56 dB depending on tape formulation.
• The peak of professional analog magnetic
  recording tape technology reached 90 dB dynamic
  range in the midband frequencies at 3
  distortion, or about 80 dB in practical broadband
  applications.

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• Digital audio at 16-bit resolution has a
  theoretical dynamic range of 96 dB, but the
  actual dynamic range is usually lower because of
  overhead from filters that are built into most
  audio systems.
• Audio CDs achieve about a 90-dB signal-to-noise
  ratio.

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• What is the Dynamic Range of a 24-bit recording?
• 144 dB! (Compared to 96 dB in 16-bit)
• Limited only by your gear!

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• The SACD format is capable of delivering a
  dynamic range of 120 dB from 20 Hz to 20 kHz and
  an extended frequency response up to 100 kHz,
  although most currently available players list an
  upper limit of 8090 kHz.
• SACD 120dB
• Human ear 120dB

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What does it all mean?

• The dynamic range from a given signal source is
  limited by the WEAKEST signal in the chain
• Mic ? Pre-amp ? Converter ? digital or analog
  medium
• Getting closer to 120dB means that our ears will
  hear the full dynamic range