An introduction to computer audio
An active crossover gets its input from the pre-amp and sends the signal to multiple outputs, each connected to a power amp.
Each power amp drives only one driver.
As the passive crossover is removed out of the power circuit, the amp has now full control over the driver (damping).
The crossover is working on line level. This allows the use of active components (opamps).
This allows for more functionality than possible with passive components.
Crossovers are covered in more detail here.
Active crossovers can be implemented using an analog circuit or using DSP.
The Model 10B features independently selectable crossover points for high-pass and low-pass, in case the speaker installation requires slightly overlapped, (or slightly staggered), response curves for the drivers. You can also independently select crossover slope, from 6, 12, or 18dB/Oct., where one driver requires faster cutoff than another in the same system. A fixed frequency plug in Linkwitz-Riley alignment with steep rolloff curves of 24 dB/Oct. is also available.
DSP is using a processor to implement the crossover.
Instead of analog components, why not use a processor.
Playing Redbook audio (CD) is 44.100 sample a second.
Obvious the processor has 1/44100= 0.000023 of a second to do the processing.
In case of 192 kHz this is 0.000005 s.
Obvious a DSP chip must be fast.
The word length is also important to avoid audible artifacts due to quantization errors.
The HDP must be placed between the pre- and the power amp.
The signal from the pre-amp is converted to digital.
The DSP is applied and the result is converted by the DACs.
DCN28 is a digital crossover, pre-amplifier and room correction in one unit.
DCN28 is supplied with the XOverWizard II advanced software which is a graphical tool to manipulate with inputs, outputs, gain, crossover frequencies, crossover slopes, equalization and delay. The software features measurement engine, post processing tools, optimizer engine with target option, output listing and direct transfer to the crossover setup environment.
Most active crossovers expect a analog input.
If the crossover is done using DSP inevitably the analog input has to be converted to digital (AD) first. Then the DSP is applied. The resulting signals are send to the DAC’s and converted to analog again.
If your audio is digital you can save two DA – AD conversions if the active crossover uses DSP and accepts digital inputs. Holm is one of the very few I know applying the DSP straight on the digital input.
However it also accepts analog inputs. They have to be AD'ed first of course.
Valid Q1 2010
DSPre 1, 1-way, Analog out
DSPre 1, 2-way, Analog out
DSPre 1, 3-way, Analog out
DSPre 1, 1-way, Digital out
DSPre 1, 2-way, Digital out
DSPre 1, 3-way, Digital out
A 9.2-Channel Network A/V Receiver with active crossover implemented in DSP.
A good explanation: What is a Digital Processing Crossover Network?
A true digital amplifier, accepting PCM input and using PWM (Pulse Width
Modulation) to amplify.
The M/S-2150 XDM crossover package is designed to support front panel crossover design, thus totally eliminating the need for computer interface. All crossover filter design algorithms are implemented in the M/S-2150 XDM internal processing unit. Crossover filters are designed and loaded in a split of a second for immediate listening and evaluation.
Supported crossover filters are Butterworth and Butterworth squared
All filter cutoff frequencies can be set anywhere between 10 and 24 KHz with a resolution of 1 Hz and with filter slopes from 6 to 72 dB/octave.
As it is a 2 channel amp you can only use this with 2 way speakers.
You need 2 amps to drive a 2 channel 2 way speaker setup.
Amps can be synchronised.
• multi-point measurements of all loudspeakers
• time-frequency analysis: the loudspeaker and the room are separately equalized
• automatic optimization of amplitude and phase response according to target curves
• intelligent active crossovers: automatic alignment of delays and gains for every driver
Freq Response: +/- 0.1dB (20 to 30kHz)
Dynamic Range: 115 dB typ (unweighted)
CMMR: >100dB (50 to 10kHz)
Crosstalk: < -100dB
Distortion: 0.002% (1kHz @ +4dBu)
Digital Audio Performance
Processor (DSP): 40-Bit Floating Point
Sampling Rate: 96kHz
Analog Converters: Super Performance 24-bit
Propogation Delay: 1.5ms
1.75 – 7.75ms with FIR
Audio Control Parameters
Gain: -40 to +15dB in 0.25 dB steps
Delay: Up to 650 ms per I/O
Variable Equalizers: 8 per I/O
Type: Parametric, Hi-shelf, Lo-self,
Phase (1st and 2nd order)
Gain: -30 to +15dB in 0.25dB steps
Bandwith: 0.02 to 2.50 Oct (Q=0.5 to 72)
Graphic EQ: 1 per Input, 31 Band 1/3 Oct steps
IIR Filter Type:
2 Individual filters per input & output.
Type - Butterworth, Linkwitz-Riley & Bessel.
FIR Filter Type:
2 Individual filters per Output.
Type - Multi-Tap.
Slopes: 6 to 48dB per Oct for IIR
50 to1200 Taps for FIR
A multi-channel soundcard and the appropriate software allows you to do the DSP on a PC.
The Building of a Pure Digital System by Arthur Cheng gives a detailed description how to do it.
The Loudspeaker Frequency Allocator is a 4-way, stereo DSP loudspeaker crossover that works with ASIO compatible multichannel sound card. Layout of each crossover leg is consistent with the way professional loudspeaker design software packages work. User is not limited to pre-canned filter algorithms such as B3 or LR4 that are so prevalent in the available hardware and software crossovers on the market today. Instead, we provide a series of flexible processing blocks that can be individually optimized to deliver the best match for the loudspeaker drivers used. Textbook filter settings are of course possible (either through direct input or by recalling factory patches), as are a vast range of other settings.
A brief list of features:
(((acourate)))® delivers both state-of-the-art digital room-correction and speaker driver-time-alignment, linearization & crossover execution in an upgradable, customizable pc-based solution.
A single user license for private, non-commercial use of (((acourate)))® is 340 € (incl. VAT)
You can do a lot with Acourate
Mitcho has an excellent walkthrough.
JRiver’s DSP studio allows you to add all kind of filters.
The low-pass and high-pas filters are Butterworths filters.
You can use this to build an active crossover.
Using the convolution engine you can apply room correction.
The DCN23 Kit is a stereo/dual mono 3-way stand alone digital crossover.
• High performance Burr-Brown converters
• 24bit resolution
• 96kHz sampling frequency
• XOverWizard software
• Optical isolated USB interface
• 48 biquads total processing filters
• 76bit processor precision
• 21mS total delay option
• Latency 1ms
• 4 layer high performance PCB
• Decoupling at all active components
The module has two 400Watt UcD modules implemented and is also available with a digital audio input AES/EBU, called the PSC2.400d version. The supply voltage is provided by a Switched Mode Power Supply (SMPS400) module, also a module from Hypex Electronics.
A PC controls the PSC2 through the USB port. This connection is used to upload the configuration and filter settings. It will also be possible to update the firmware through USB.
The “DLCP” is a complete hardware/firmware platform for digitally filtered (6 channels) and corrected active multiway loudspeakers. Digital response correction allows significant extra degrees of freedom in the acoustic design of a loudspeaker. Driver parameters can be selected for best efficiency and distortion instead of electrical damping, and the cabinet can now be fully optimized for radiation pattern.
Digital Signal processing
|28/56 bit Digital Processor - Double precision processing|
|Host processor||48MHz micro-controller|
|Sample rate||48/96/192kHz (depending on the plug-in configuration )|
|ADC/DAC resolution||24 bits|
|Analog audio input||Unbalanced signal, RCA terminated, 2 x Inputs|
|Maximum input level, THD<1%||0.9Vrms (RevA) or 2Vrms (RevB)
|Dynamic range, un-weighted
|Analog audio output||Unbalanced signal, RCA terminated, 4 x Outputs|