Advanced Lecture

 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. d.html+dynamic+range+ovu+nominal+dbfs&cd=1&hl=en&ct=clnk&gl=us&client=firefox-a

 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!

 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.

 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.

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.

 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.

 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.

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

 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.

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.

 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.

 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.

 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

Dynamic Range Comparison  AM Radio dB  FM Radio dB  Vinyl microgroove phonograph records typically yield dB, though the first play of the higher-fidelity outer rings can achieve a dynamic range of 70 dB.

 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.

 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. [ [

 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.

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

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 80–90 kHz.  SACD – 120dB  Human ear – 120dB

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