Setting Up DSP Processors Gordon Moore CTS Gordon

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Setting Up DSP Processors • Gordon Moore CTS • • Gordon. moore@lectrosonics. com 1

Setting Up DSP Processors • Gordon Moore CTS • • Gordon. [email protected] com 1 -800 -821 -1121

DSP § Digital Signal Processors § Can be any device that modifies a digital

DSP § Digital Signal Processors § Can be any device that modifies a digital signal (video, audio – anything) § In this class – we will be talking about Audio § NOT a “How-to” for specific manufacturers § Use their training

§ Apologies to any Manufacturers whose screens are not featured – no slight intended.

§ Apologies to any Manufacturers whose screens are not featured – no slight intended. § The CONCEPTS are the core of this course - no brands endorsed or rejected.

What to expect § Signal pathway organization § Setting the array of “modules” or

What to expect § Signal pathway organization § Setting the array of “modules” or functions available

Why? § Most DSP processors are barely used to their best capability. § Units

Why? § Most DSP processors are barely used to their best capability. § Units returned for service usually have just the simplest functions enabled while many enhancements are not touched.

Most commonly unused or forgotten § § § Compressors Limiters Input filtering NOM bus

Most commonly unused or forgotten § § § Compressors Limiters Input filtering NOM bus Delays

Most commonly set up functions § § Input Gain (But often badly set) Routing

Most commonly set up functions § § Input Gain (But often badly set) Routing (inputs to outputs) Equalization for outputs Controls interfaces

DSP organization § Flexible Architecture § Fixed Architecture § Dedicated function (one capability only)

DSP organization § Flexible Architecture § Fixed Architecture § Dedicated function (one capability only) § Multi-function with fixed pathway Hybrid Architecture – some fixed, some flexibility in routing

Flexible Architecture All functions can be configured in a “drag-n-drop” environment. Audio functions can

Flexible Architecture All functions can be configured in a “drag-n-drop” environment. Audio functions can be placed almost anywhere along the signal chain in any order. Characterized by a drag and drop GUI (Graphical User Interface) and/or “fuel gauge”.

Sample

Sample

Advantages Complete flexibility – you can do some amazing things within a single box

Advantages Complete flexibility – you can do some amazing things within a single box and develop very complex signal paths. Excellent choice for systems where complexity and/or multiple applications may come into play. Airports Large scale paging systems Complex communications systems Very little you cannot accomplish.

Disadvantages § Flexible Architecture may be more costly on a per channel basis §

Disadvantages § Flexible Architecture may be more costly on a per channel basis § Requires more DSP power – memory register stacks must be allocated for any eventuality – code space cannot be optimized.

Fixed Architecture § Dedicated function § Does one type of function § Compression/limiting §

Fixed Architecture § Dedicated function § Does one type of function § Compression/limiting § Or § Equalization § Or § Signal Routing

Advantage Fixed architecture is simple to set up and operate – may not even

Advantage Fixed architecture is simple to set up and operate – may not even require a computer Less cost for the box – may not be as cost effective as a combined DSP capability Sets up much like analog counterpart Excellent choice for existing system upgrade

Disadvantage § Very limited in scope of function § May not be very scalable

Disadvantage § Very limited in scope of function § May not be very scalable

Fixed Architecture Multi-function Has multiple functions in a fixed pathway Generally fairly cost effective

Fixed Architecture Multi-function Has multiple functions in a fixed pathway Generally fairly cost effective Limited in terms of routing and or set up choices. Advantage – predictable known good pathway No gauge Disadvantage – few if any routing choices

Hybrid Architecture § Combination of routing choices plus fixed multiple function signal pathway §

Hybrid Architecture § Combination of routing choices plus fixed multiple function signal pathway § Advantages – § Allows flexibility as far a signal routing goes – what inputs show up at what outputs § Optimizes DSP processing power – memory stacks and registers can be more tightly packed § Disadvantages § May not fulfill all needs in a system

Hybrid Architecture

Hybrid Architecture

Enough Boring stuff – Let’s set up some functions § § Input Gain Filters

Enough Boring stuff – Let’s set up some functions § § Input Gain Filters – Input and/or Output § § § Equalization Feedback suppression Crossovers Noise reduction Dynamics § Compressors § Limiters § Gates § Routing

Dynamics § Those functions affecting gain structure and levels

Dynamics § Those functions affecting gain structure and levels

INPUT GAIN § § § Most important setting – GET THIS RIGHT! Always set

INPUT GAIN § § § Most important setting – GET THIS RIGHT! Always set up – but not necessarily well set up Microphones § Handheld Vocals = 35 d. B minimum § Handheld Presentation = 45 d. B § Gooseneck desk = 45 d. B § Boundary mic = 55 d. B § Any further away = 60 db+ § Ceiling – as hot as you can get it

INPUT GAIN § Multimedia § Unbalanced? Consumer = +10 § Balanced? Professional = 0

INPUT GAIN § Multimedia § Unbalanced? Consumer = +10 § Balanced? Professional = 0 to -8

Signal to noise ratio Poor S/N Ratio Line Level Mic Level Noise Floor Mic

Signal to noise ratio Poor S/N Ratio Line Level Mic Level Noise Floor Mic Preamp Mixer Signal processors Amps

Signal to noise ratio Line Level Mic Level Noise Floor Good S/N Ratio Mic

Signal to noise ratio Line Level Mic Level Noise Floor Good S/N Ratio Mic Preamp Mixer Signal processors Amps

Signal to noise ratio Line Level Mic Level Noise Floor Mic Preamp Mixer Signal

Signal to noise ratio Line Level Mic Level Noise Floor Mic Preamp Mixer Signal processors Amps

THRESHOLDS § The level at which the desired function becomes active § Generally speaking

THRESHOLDS § The level at which the desired function becomes active § Generally speaking a lower threshold level means it will activate earlier. § Recommended starting threshold for most line level (post preamp) functions = 0 d. Bu

AGC and/or Levellers § § Automatic Gain Control RAISES gain if signal too low

AGC and/or Levellers § § Automatic Gain Control RAISES gain if signal too low Compresses if signal too high BE VERY CAREFUL with these § Can run a room into feedback if used on amplified inputs § Primary application – to capture weak signals for recording or transmission § Start with threshold set at 0 d. B – keep gain centered at line level

Ambient Level Control Uses a reference microphone to measure room noise level that automatically

Ambient Level Control Uses a reference microphone to measure room noise level that automatically adjusts system for noisier environment Reference microphone may be dedicated microphone – only purpose is reference, or may be designated microphone – used in system but designated to be the reference signal Read the manual

COMPRESSORS § § Control dynamics - loudest to softest Useful for keeping level under

COMPRESSORS § § Control dynamics - loudest to softest Useful for keeping level under control Meek versus motivational speaker Rarely set up

Compressor settings - Ratio § Ratio – The amount of actual level increase above

Compressor settings - Ratio § Ratio – The amount of actual level increase above threshold that will yield ONE decibel in actual gain change after the compressor. § Example – 3: 1 ratio § For every 3 DB the gain increases above threshold, the final level will change only one d. B § SO, if level jumps 9 DB, the final level will jump only 3 d. B § FM is broadcast at typical 10: 1 ratio

Compressor settings – Threshold, Attack, Release § Threshold - Level at which compressor begins

Compressor settings – Threshold, Attack, Release § Threshold - Level at which compressor begins to engage and affect level. § Attack – time in milliseconds the compressor begins to make changes after level exceeds threshold § Release – time in milliseconds the compressor lets go after level settles below threshold. § Makeup or post compressor gain § Compensation in level to make up for compressor reduction in signal.

Suggested setting for compressors § Speech systems (conference rooms, boardrooms, etc) Ratio = 3:

Suggested setting for compressors § Speech systems (conference rooms, boardrooms, etc) Ratio = 3: 1 Attack = 10 -20 ms Release = 200 -500 ms Threshold = 0 If initial input gain was set to result in 0 d. B level, then it would take a 60 d. B increase at the mic to hit the +20 d. B limit of input (clipping) MUSIC or Multimedia – try increasing ratio to 6: 1 BE CAREFUL – too much = bad

LIMITERS § Basically, a compressor with an infinite ratio § Absolute ceiling to maximum

LIMITERS § Basically, a compressor with an infinite ratio § Absolute ceiling to maximum level § Protects downstream gear by preventing severe clipping and overdriving amps and speakers § Many amplifiers have built in limiters to protect themselves. § ALWAYS set limiter threshold above threshold of compressor § Otherwise, compressor will never engage § Good for spikes like dropped microphones, cymbals, plosives (P, D, T)

Suggested Limiter settings § Threshold – 15 db higher than compressor = +15 d.

Suggested Limiter settings § Threshold – 15 db higher than compressor = +15 d. B if 0 d. B for compressor § Attack – faster than compressor = 2 ms or quicker § Release – 200 ms or less

Some dynamics filters can be frequency specific § Compressor with low pass filter good

Some dynamics filters can be frequency specific § Compressor with low pass filter good for controlling proximity effect while allowing high frequencies to pass unaffected.

EXPANDERS § Increases gain if signal very low such as weak talker § BE

EXPANDERS § Increases gain if signal very low such as weak talker § BE VERY CAREFUL HERE – Expanders, in an amplified environment, can push system into ear bleeding feedback. § Primarily intended for recording and or transmission.

GATES § Gates activate a channel, allowing it to pass, once the level passes

GATES § Gates activate a channel, allowing it to pass, once the level passes above threshold. § Found in some automixers § Useful for noise control (noisy multimedia source, for example) § Originated in music

Attack , Release, Threshold § Attack – try relatively fast settings, 1 ms to

Attack , Release, Threshold § Attack – try relatively fast settings, 1 ms to begin § Release – start at 50 ms § Threshold – depends on place in chain § If after input gain – 0 d. B is a good starting place § Lower if not getting a reliable start

Noise Gate

Noise Gate

Spectral § Affects the frequency response of the system

Spectral § Affects the frequency response of the system

EQUALIZATION (Inputs) § Equalization is one of the most commonly used functions § Input

EQUALIZATION (Inputs) § Equalization is one of the most commonly used functions § Input EQ is generally for tonality control – adjusting the tonal content so each input sounds similar.

EQUALIZATION (Outputs) § Generally used for speaker compensation § Adjusting for “quirks” or characteristics

EQUALIZATION (Outputs) § Generally used for speaker compensation § Adjusting for “quirks” or characteristics in the loudspeaker response. § You cannot EQ a “room”

Equalization patterns § § Pass – Low, High or Band Shelving – Low or

Equalization patterns § § Pass – Low, High or Band Shelving – Low or High Parametric - Notch Graphic

“Q” § No, not James Bond’s gadget guy § The ratio of filter width

“Q” § No, not James Bond’s gadget guy § The ratio of filter width to depth at 3 d. B roll off points

Low Q – Wide band width

Low Q – Wide band width

High Q – Narrow Band width

High Q – Narrow Band width

Filter Slope or “Order” § Rate of attenuation on filter - Shown in terms

Filter Slope or “Order” § Rate of attenuation on filter - Shown in terms of d. B/octave § Octave – doubling of frequency § § § First order = 6 d. B per octave Second Order = 12 d. B per Octave Third Order = 18 d. B/Octave Fourth Order – 24 d. B/Octave Each order equals another 6 db of roll off. § That means 4 times factor in power level § If 6 db down from 100 watts = 25 watts.

First Order – 6 d. B per octave (High pass)

First Order – 6 d. B per octave (High pass)

Same filter – Second order

Same filter – Second order

Eighth Order- 48 d. B/octave

Eighth Order- 48 d. B/octave

Parametric § § Fully configurable Boost or Cut adjustable Center Frequency selectable Q selectable

Parametric § § Fully configurable Boost or Cut adjustable Center Frequency selectable Q selectable

Parametric

Parametric

Band Pass

Band Pass

Low Pass

Low Pass

High Pass

High Pass

Shelving – Boost or cut, High or Low

Shelving – Boost or cut, High or Low

Filters - Graphic EQ

Filters - Graphic EQ

CROSSOVERS § Used for bi-amplified and tri-amplified systems § Low frequency content sent to

CROSSOVERS § Used for bi-amplified and tri-amplified systems § Low frequency content sent to bass amplifiers § Mid and high range sent to appropriate amplifiers § § § Separate amplifiers involved Large scale concert systems High order - 4 th to 8 th order filters Bass – 250 Hz or lower For tri-amplified – start at 4 K for high pass

FEEDBACK SUPPRESSION § Should be set up LAST after Equalization § Smooth response FIRST,

FEEDBACK SUPPRESSION § Should be set up LAST after Equalization § Smooth response FIRST, then take care of Feedback nodes § A time domain issue coupled with Frequency domain § Notch Filters – very tight § But too many can badly affect content

Set up tip – One mic at a time § 1. Before final EQ

Set up tip – One mic at a time § 1. Before final EQ – run feedback “eliminator” first § 2. Make note of first three feedback freqs § 3. Construct three very tight notch filters at INPUT on those frequencies § 4. Reset the feedback filters § 5. engage feedback filters again after equalization and system is at operational levels.

NOISE REDUCTION § Popular new algorithms that “sample” the noise floor § Noise floor

NOISE REDUCTION § Popular new algorithms that “sample” the noise floor § Noise floor – acoustical and electronic noise that is NOT wanted in system § Air Conditioning § Fan noise § Laptops near boundary mics § computers § Projectors § Electronic noise – noisy sound cards in computers etc.

Setting Noise Reduction Filters § § Canceller Depth – depends on the amount of

Setting Noise Reduction Filters § § Canceller Depth – depends on the amount of noise Quiet conference room with little to no noise may not need this. Computer and projector fan noise – try starting at 9 d. B. Heavy room noise – large attendance training room or bad air conditioning rumble, try 12 d. B § Remember, these filters remove spectral content – none are perfect and they will affect your room response. § DON”T GET CARRIED AWAY!

Signal Generators § § White noise – equal energy per frequency Pink Noise –

Signal Generators § § White noise – equal energy per frequency Pink Noise – equal energy per octave Tones Primary use – test and measurement § Use pink noise to set up your levels in the room § If your gain structure is correct – this will allow amplifiers settings to be accurately set up § Use test tones for gain staging and/or speaker alignment § Secondary Use § Noise masking – covering conversation or background ambient noise § Alarms

ROUTING § Matrix – § Rarely overlooked § Determines which inputs go to which

ROUTING § Matrix – § Rarely overlooked § Determines which inputs go to which outputs § (technically speaking “gozindas to gozoudas”) § Some traps here § Watch for § Feedback loops § NOM bus assignment – VERY IMPORTANT

Selecting NOM bus and action § NOM= Number of Open Microphones § Determines interactions

Selecting NOM bus and action § NOM= Number of Open Microphones § Determines interactions of microphones in automixing § Failing to select correct NOM interaction can affect echo cancellation, and gain before feedback § Choices may include § Chairman Over-ride § Auto mix (or Normal) § Background (or Ducking)

Feedback loops § Common error in setup – requires careful documentation and double checking

Feedback loops § Common error in setup – requires careful documentation and double checking – especially when dealing with mix minus conferencing systems. Sending an input BACK to itself.

Delays § § Often neglected Primarily used for time alignment § Loudspeaker stacks in

Delays § § Often neglected Primarily used for time alignment § Loudspeaker stacks in large venues § Input alignment § Loudspeaker alignment § Secondary use for spatial referencing (Haas effect) § Localization of sound based on first heard § Set up tip – § Try setting for 10 ms or 10 ft or 3. 3 m FARTHER than distance would indicate. § Example – Speaker is 68 ft from stage – instead of 60. 5 ms, try 70. 5.

Some architectural Do’s and Don’ts § In Flexible Architecture – General rules – always

Some architectural Do’s and Don’ts § In Flexible Architecture – General rules – always exceptions § Do NOT put compressors before Equalizers/Filters § The EQ can take out energy that would falsely trigger compressor – so put compressor AFTER filtering § Do NOT put limiters before compressors § Do NOT put limiter thresholds lower than other devices – especially compressors § Be careful about thresholds for automixers – (gated designs) § Too low and room noise will open mics § Too high and you may lose the first characters § Shared gain mixers will not have thresholds

Hybrid Architecture Do’s and Don’t § Don’t create a feedback loop – be careful

Hybrid Architecture Do’s and Don’t § Don’t create a feedback loop – be careful where you send inputs § Don’t go overboard on settings § “Too much of a good thing is wonderful” does NOT apply here.

Troubleshooting tips § Ringing or severe echo in audio § Internal feedback loop §

Troubleshooting tips § Ringing or severe echo in audio § Internal feedback loop § Signal generators or incoming conferencing too loud § Poor input gain structure – HOT IT UP! § HISSsssss or noisssse in system § Bad gain structure – inputs too low – Amplifiers too high § University reasoning – wrong solution to the right problem. § Amps set to full output § Inputs set low § Correct solution – lock up the amplifier controls.

Questions? § Fill in your reviews please!

Questions? § Fill in your reviews please!