Safe Sound Audio P501 User Manual

P501 Audio Processor User Manual Safe Sound Audio

P501 Audio Processor

User Manual

Safe Sound Audio, UK

P501 Audio Processor User Manual Page 2

P501 Audio Processor Features

500 Series

Fully compatible with the API™ 500 Series modular format which
allows a number of audio modules to be plugged into rack frames
such as the API™ 6-slot Lunchbox and 10-slot 500VPR rack frame.

Input Stage

Wideband 60kHz high gain mic amp is partnered with a front jack
accessable balanced line input, which is also relay switchable to
become a high impedance DI input. A switchable 80Hz, 18dB/octave
hi-pass filter is included.

Compressor

Advanced audio compressor with peakride which uses multiple side­chains in tandem allowing for very musical dynamic control of source
material. Peakride compression is very easy to dial in when tracking
and evens out levels in a very musical way without robbing the sound
of life, so bringing the performance a new energy whilst remaining
transparent and not sounding overly affected. It’s especially powerful
in providing tightly controlled vocal compression with perfect
transparency. The inclusion of auto gain make-up allows you to
increase gain reduction ‘on the fly’ without having to constantly
readjust the output level.

Variable attack limiter design

Switchable fast limiter offers ultimate protection during tracking or
push it hard as a great dynamic effect especially on bass and drums.
The limiter features dynamic adjustment of attack time, so the faster
the audio front edge, the faster the limiter reacts. Fast clipping
protection when tracking but also very useful as a creative tool in its
own right when pushed into heavy levels of limiting.

Output stage

The balanced output will drive +22dBu into 600 ohms with a useful
±15dB of output gain control available.

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Contents Page

P501 Audio Processor Features 2
500 Series Compatibility 4
Installation 4
Detailed Operation Guide 5

Input Stage 6
High Pass Filter 6
Peakride Compressor 7
Peakride Compressor Design Theory 8
Limiter 10

Output Gain and Level Metering 11
Technical Specification 11
Warranty 14
How to contact us 15

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500 Series Compatibility

The P501 Audio Processor is intended for use within an API™ 500
Series compatible rack frame from which is takes its power and audio
connections. It cannot function as a stand-a-lone unit. Information
about the API™ 500 Series rack frames can be found at
www.apiaudio.com.

As the microphone input stage in the P501 has the capability to
switch phantom power, please ensure you choose a rack frame
which includes +48V phantom power as this is not generated within
the P501.

API is a registered trademark of Automated Processes Inc.

Installation

The P501 is supplied in a foam lined shipping carton and should
arrive with you in perfect condition but it is always worth checking the
unit for any signs of physical damage before use. Should you have a
concern that the unit appears damaged then contact your dealer.

Ensure that your 500 Series compatible rack frame is powered off
before inserting the P501 module. Select a spare slot and remove
the module mounting screws at that slot location. Slide the P501
module into the slot ensuring that the gold plated edge connector on
the P501 aligns with the corresponding connector in the rack frame.
Now gently push home the module until the front panel is flush with
the rack frame. Use the two screws supplied with the rack frame to
secure the module. Never use excessive force when inserting a
module into the frame, so if you are struggling to get the module to
insert, recheck the alignment and try again. Avoid touching the gold
plated edge connector as you could tarnish the connects and reduce
the reliability of the audio connection between the module and the
rack frame.

Turn on the rack frame power, connect audio and check through the
functionality of the P501 module according to the guidance in this
manual.

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Detailed operational guide

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Input Stage

Three audio input types are provided for, these are:
Balanced microphone input, for use with either dynamic or

phantom powered condenser microphones. Connect via the XLR
input connector for the corresponding channel on the rear of the rack
frame. Select switch number (7) to ‘line’.

Balanced line level input, for use with any line level source, most
commonly when using the P501 as an insert effect within the
recording or mixdown chain. Connect via the ¼” jack (9) on the front
of the P501 module. Switch number (7) selected to ‘line’.

Unbalanced instrument input, for direct injection of most electric or
bass guitars. This is sometimes called the DI-INPUT (direct
injection). Connect via the ¼” jack (9) on the front of the P501
module. Switch number (7) selected to ‘instr’.

All three input types have different gain ranges available within the
P501 to suit the type of source, all controlled from a single gain
control (2).

+48V Phantom power is selected on by selecting switch (1)
downwards. Always connect the microphone before switching on
phantom power and always switch off phantom power before
disconnecting the microphone. Always best to mute your monitoring
chain first as switching phantom power cause audible ‘thumps’
through your audio chain.

High Pass Filter

The high pass filter is sited in the audio signal path immediately after
the input stage but before the compressor and limiter. It operates at
80Hz with a slope of 18dB/octave.

Bring the high pass filter into circuit by selecting switch (3)
downwards.

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Peakride Compressor

Compressors progressively reduce the gain of an audio signal as its
input level rises above the compressor threshold as shown in the
diagram below.

The compressor threshold is the level point in dB above which the
audio gain will be reduced. On the P501 this can be varied from 0dB
to -40dB using the T/HOLD control (12).

The ratio control (4) varies the degree of gain reduction which is
applied, from 1:1 (no effect) to  : 1 which will make the compressor

act like a limiter.
The attack time is how quickly the compressor will react to audio

which rises above the threshold point. In the P501 the attack time
can be varied from 60ms (slow) to 1ms (fast) using the ATTACK
control (11). The setting of the attack time usually has a large impact
on the compression effect.

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The release time is how quickly the compression effect is removed
when the audio falls back below the threshold. The P501’s release
time is programmed to follow the dynamics of the falling audio level.
This is an important aspect of the P501’s compressor design and
offers a very natural sounding form of compression.

The amount of gain reduction (due to the compressor and limiter) is
shown in the 6 segment LED meter (13).

Bring the compressor into circuit by selecting switch (5) downwards.
Because compression is a gain reduction tool, it will tend to lower the

maximum audio level through the audio chain. Make-up gain is used
to replace this ‘lost’ level and in the case of the P501 this is done
automatically; the amount of make-up gain applied being related to
the threshold and ratio setting. Auto gain make-up is really useful as
it allows you to increase gain reduction ‘on the fly’ without having to
constantly readjust the output level.

Peakride Compressor design theory

With so many analogue and digital compressors on the market
today, we decided to try a new approach to single audio band
compression which gives most of the advantages of multi-band
compressors (plus a few more!) without the operational complexity of
band splitting. The full story of peakride compression is told in our
design white paper but here are the highlights;

It’s desirable for a compressor to be able to offer a wide range of
attack and release times to suit a variety of source material. For
example, percussion typically requires medium fast attack and
release times whereas some vocals require quite fast attack times
and medium/slow release times. Fast attack, fast release
compressors often have poor audio performance especially distortion
caused by ripple of the side-chain by the audio. Have a look at the
diagram below;

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Notice that the pure tone audio signal is beginning to lose its smooth
top and bottom curves and begins to resemble a triangular
waveform. This is not just an issue for bass guitar and bass drum
compression. Many audio sources including piano and vocals have
either a primary low frequency ‘carrier’ component and
vibrato/tremolo induced low frequency components. All can cause
audible distortion when being compressed or limited.

The peakride design overcomes these problems by the use of three
separate control side-chains which act in the time domain (rather
than in the frequency domain of a multi-band compressor).

Above the compressor’s threshold;

Short duration audio bursts (such as percussion) get processed with
the fast attack fast release compression which they tend to require.

Longer duration audio bursts get processed with an initial attack time
as set on the front panel and an initial short release time but; as the
audio sample continues, the attack and release times are
progressively lengthened according to two factors;

 The time the audio sample has been above the compressor

threshold

 The continuing dynamics of the audio signal

A second problem with traditional fast attack compressor designs is
caused by a misunderstanding between the desirability for fast
attack, especially to provide adequate control of certain vocal styles,

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and the usual consequence that the whole vocal phrase then suffers
from over compression. It is often difficult to achieve the attack
speed without the undesirable over compression.

The peakride compressor achieves this by altering the ratio of the
compressor dynamically. So you can set an average compression
ratio on the front panel control but the actual delivered ratio will alter
to suit the dynamics of the audio as it rises above the threshold level.

These principles are at the heart of the peakride design and are
achieved by mixing the three compressor side-chains at different
levels and with different compression ratios. In effect, the
compressor side-chain is able to ride the peaks of the audio, reacting
quickly but smoothly to fast attack peaks, and then able to track the
dynamics of the continuing audio till it falls below the threshold point.

Limiter

The P501 includes a switchable audio limiter which can be used to
prevent digital clipping in your recording chain. The limiter is sited in
the audio signal path immediately before the output level control and
operates at fixed threshold of +6dBu (nominal).

The limiter features dynamic adjustment of attack time, so the faster
the audio front edge, the faster the limiter reacts. So fast clipping
protection when tracking but also very useful as a creative tool in its
own right when pushed into heavy levels of limiting.

We’ve added a programme tracking release circuit which provides for
very smooth recovery from limiting, adapting to the natural dynamics
of the audio source.

Bring the limiter into circuit by selecting switch (6) downwards.

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Output Gain and Level Metering

The output gain control (8) is sited in the signal path immediately
after the limiter and just before the final balanced output stage which
in turn feeds the audio output to the selected channel output XLR in
the rack frame. The most common use of the output gain control is
to match the peak output level of the P501 to the peak input level of
your recording device. Once you have done this level matching it’s
usually not necessary to alter the output gain control during
recording.

The P501’s level meter (10) is intentionally placed BEFORE the
output gain control. We suggest you use the level meter in
conjunction with the INPUT gain control during recording set-up so
that the maximum audio level during tracking is lighting one or both
of the yellow level LED’s but not intentionally lighting the red level
LED. When switched into circuit the P501’s limiter will keep the
maximum output level below 0dB (nominally +6dBu).

Operating at higher nominal recording levels (e.g. +18dBu) is also
possible by switching the P501 limiter off and using only the
recording meters in your recording device to monitor the maximum
desired recording level.

Technical Specification

P501 AUDIO PROCESSOR

Physical

Size : API™ 500 Series Compatible (38mm

wide by 133mm high by 150mm deep)
Weight : 0.4kg (0.9lbs)
Power requirements : ±16 volts dc at ±120mA to the

standard API 500 Series pin-outs.
+48 volts dc for phantom power

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Fusing : On board ‘auto reset’ polyfuses
protecting the ±16V and +48V rails

Main processor audio path

Frequency response : -0.5dB points at 5Hz and 60kHz
Distortion : < 0.01% at 1kHz (typically 0.008%) main

signal path working at 0dBu

Maximum input levels

Microphone : +12dBu
Line input : +22dBu
Instrument : +18dBu (when fed unbalanced)

Input impedances

Microphone : 2k4 ohms
Line input : > 10k ohms
Instrument : 1M ohms

Equivalent input noise figures

Microphone : 128dB (max gain with 150 ohms source)
Line input : 100dB (unity gain)
Instrument: 105dB (max gain)

High Pass Filter
Switchable 80Hz hi-pass filter with 18dB/octave slope

Balanced Line Output

Output Gain : ±15dB (post limiter)
Maximum Output Level

(post limiter) : +22dBu
Output impedance: 50 ohms

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Output Noise : -93dBu RMS unweighted,

measured 22Hz to 22kHz

-95dBu RMS A-weighted,
measured 22Hz to 22kHz

Input Gain Ranges

Microphone input : 0dB to +72dB
Line input : -10dB to +20dB
Instrument input : +2dB to +33dB

Peakride Compressor

Threshold range : 0dB to -40dB
Attack time range : 60ms to 1ms
Release time : variable from 90ms to 500ms (tracks the

natural audio decay)
Ratio : 1:1 to INF:1
Make-up gain : automatically set in proportion to the

threshold and ratio settings
Gain reduction meter : calibrated in dB’s

Dynamic Attack Limiter

Threshold : fixed internally to +6dBu (nominal)
Attack time : audio related with a fastest response of

0.5ms
Release time : audio related from 50ms to 500ms

Metering

Level metering : 6 element LED display measuring -21dB to
0dB (0dB equates to Limiter Threshold)

Gain Reduction : 6 element LED display

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Warranty

Safe Sound Audio provides a 12 month warranty from the purchase
date according to the following conditions;

This warranty is not transferable and applies only to the original
purchaser of the unit.

If the unit should become faulty, then contact Safe Sound Audio or
your local distributor for a Returns Authorisation Number. No items
will be accepted for warranty repair without this authorisation
number.

You must be able to produce proof of the purchase date.
If the returned unit should prove faulty then, at Safe Sound Audio’s

choice, we will either repair or replace the unit.
The customer is responsible for the cost of sending the unit back to

Safe Sound Audio or our authorised distributor including insurance of
the unit during shipping.

Safe Sound Audio or our authorised distributor will be responsible for
the cost of shipping the repaired or replaced unit back to the
customer including insurance of the unit during shipping.

The warranty will be void if the unit has;

 Suffered physical damage.
 Been repaired or modified by anyone other than Safe Sound

Audio or its authorised representative.

 Has been connected to an incorrect source of power.
 Has been damaged due to liquid spillage.

Safe Sound Audio shall not be liable for any special or consequential
damages resulting from the use of this product.

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How to contact us

By post : Safe Sound Audio

47 Broadgate Lane
Horsforth
Leeds
West Yorkshire
LS18 4AG
UK

Callers strictly by appointment

By telephone : [phone]

By e-mail : [e-mail]

On the web : www.safesoundaudio.com

Safe Sound Audio reserves the right to make changes and

improvements to the design of this product without notice.

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© Safe Sound Audio 2009