Supporting any speaker with the best working conditions is no trivial task. Traditionally speakers use analog crossovers to filter the right frequency range to the corresponding speaker-units. These analog filters have to be rather complex to support the speakers for optimum performance. Back-draw to the analog filters are that they are mounted between the power-amplifier and the speakers motor and this leads to a situation where the amplifier loses contact or control over the speaker-units. To overcome this situation we at HOLM acoustics have been able to rule out analog filters in the speakers by driving each speaker-unit from its own power-amplifier and do the crossover filtering in our preamplifier DSPre 1. Our preamplifier is a digital signal processing platform with up to 6 channels of high performance signal processing, covering separate stereo outputs for bass, mid-tone and treble. Each preamplifier output drives its own power-amplifier who again drive its own speaker-unit. Having direct control over each speaker-unit separately leads to a wealth of opportunities in correction and equalization. Correction that can be used to correct parameters on every speaker unit at its own and not only the system as a whole - every membrane will be driving at optimal working conditions.

DSPre 1 is the perfect tool for unveiling the best performance of your speakers and listening room.

Some of the strong features are:
- DSPre design.
- DSPre software DSPreLab.
- Room adaption. - NEW!!
- Individual filtering and correction of every driver.
- Perfect summing of driver outputs.
- Calibrated measurement microphone.
- Jitter removal from any digital source - "Clock Flawless" system.
- USB audio playback and recording of any input.
- Digital inputs TOSLINK, SPDIF, AES/EBU.
- Analog to Digital inputs natively, no extra cost for A/D modules.
- 6 analog outputs for stereo bass, mid and tweeter.
- Band-less equalizer to tune to your preference.

DSPre design:
The DSPre unit is designed with the objective to have the least clutter in terms of controls. Only four buttons for shifting source and adjusting volume is on the front plus a combined "IR window and stand-by" button in the middle of the "O" in the HOLM brand name. A dimmable VFD display shows input source in text of your own choosing, sample-rate of your source and what filter is active in the DSPre. All other control of the quite advanced DSPre is done from the PC software DSPreLab. The cabinet is made from 6 mm thick hand-polished black anodized aluminum. The buttons are embossed into the leather belt running 3 sides of the cabinet.

DSPre software DSPreLab:
DSPreLab is the full featured PC application that transforms DSPre to a comprehensive speaker measurement tool and hold the power to transform these measurements into state of the art digital filters to run real-time on the DSPre. No PC needs to be connected during normal playback. The filter-type run on DSPre is FIR "Finite Impulse Filter" hence the name DSPreLab. FIR filters holds the unique property having arbitrary amplitude and phase response, which means amplitude can be filtered without altering the phase and vice versa. This gives the ability for making filters that corrects all linear errors in speaker-units and gives the speakers the ability to reconstruct the exact waveform recorded on your media. Taking this concept further makes way for perfect summing of signals from several speakers-membranes and recreate perfect impulse-response also in multi-way systems. DSPreLab yields a graphical interface for adjusting Crossovers, Gains, Driver-corrections, time align, Room adaption, Equalization, DSPre hardware-settings, display texts etc. Click here to learn more about DSPreLab

Room adaption: - NEW!!
The newest addition to our software is our Room adaption tool. The tool assists the user or setup technician in the creation of a stereo equalization that will compensate for the frequency dependant reverberation time of any listening room. Like most other Room correction/adaption systems our is set up by a simple walk-through wizard that acquires the measurement-data that is the basis for adaptation and calculates an inverted room response. Unlike most other systems our room-adaption can be adjusted by the user by terms of frequency range, maximum gain/damping, sweet-spot priority, filter sharpness and how tight the inverted room response shall be. This way there is a a high degree of freedom how your room and speakers interact, killing your listening room is not always what you want to do.

Individual filtering and correction of every driver:
The mechanics of speaker drivers are far from optimal in regards to reproducing sound and music. Speakers do not generate a sound-pressure who is equal at every frequency neither the phase or group-delay of the speaker is the same at every frequency. The DSPre can correct this by measuring the near field impulse response and calculate a impulse correcting filter using the DSPreLab software and a measurement microphone. This way each speaker-unit can be corrected for whatever amplitude of phase imperfections they have. Since DSPre holds 6 FIR Digital signal chains and up to 3 pcs stereo DAC outputs it is possible to sustain a fully active crossover 2 or 3 way system or conventional passive filter speaker. In our active filter systems each membrane of the speaker is driven by its own dedicated FIR filter DAC and power-amplifier, and every driver can be filtered individually. The crossover can be set at arbitrary filter order and arbitrary crossover frequency. Since the filter-type is FIR, no phase distortion is applied in the basic filter. By physical properties, all dynamic drivers has both amplitude and phase distortion. These distortions can be corrected in the FIR filters.

Perfect summing of driver outputs:
Using phase and amplitude corrected filters is a clear advantage since both drivers in the crossover region has the exact same phase response and inverse amplitude response. Same phase and inverse amplitude means perfect summing of contributions from each speaker-membrane, no amplitude or phase distortion is detectable in the crossover region. Pre and post ringing of filters of all filters cancel perfectly and a immaculate impulse response can be achieved on multi-way systems. After correction of the amplitude and phase the summation of sound from each driver unit can be easily obtained by time-aligning in the listening position. The time-aligning process is done by acoustic measurement (no measuring tape is used) the speakers can be time-aligned to a precision of below 0,2mm - at the listening position. 0,2mm corresponds to a phase-error of 5 degree for a 3kHz crossover. The average analog crossover speaker has a phase-distortion of several hundred degrees.

Calibrated measurement microphone:
Add on product to DSPre is a calibrated measurement microphone MIC 1. To make impulse correct measurements on the speakers we had to develop our own microphone and have this both amplitude and phase calibrated to our specifications. The mechanics of the microphone is special in that the microphone has minimal reflection in itself. Most measurement microphones has a somewhat short neck and a thicker body, who will make an early reflection in the 0.5 to 2 millisecond range after the initial sound-wave. Our has none, and thus it makes sense making wide-band amplitude and phase calibration since this will be consistent in most directions. No other commercial audio brand has a amplitude and phase calibrated microphone at our standard.

Jitter removal from any digital source - "Clock Flawless" system:
To cope with Jitter (Digital time noise) picked up on cables or generated in your media source we have invented the "Clock Flawless" system. Clock Flawless is based upon a asynchronous buffer, a digital control and loop filter and a DAC controlled voltage controlled precision crystal oscillator. The Clock flawless system operates in two modes "SRC" = Sample Rate Converter mode when the signal is non 44100Hz, and in "LOCK" mode when 44100Hz. LOCK mode is subdivided into different speeds of loop filtering a fast mode for achieving lock onto the incoming sample-rate and a slow mode when lock is established. in the slow mode the numerical value of the DAC is only updated 4 to 5 times a hour resulting in a extremely good low-frequency jitter-reduction and a resulting total jitter noise of less than 10 pico second RMS.

USB audio playback and recording of any input:
The domestic computer has grown to be one of the most used sources for music, this is why we found the most natural option was to integrate USB audio directly in the DSPre 1. The USB is used for playback of any audio format stored on your computer; wav, Flac, mp3 or Internet based radio. The DSPre has the USB connector on the rear panel and connecting this to your computer results in DSPre appearing on your computer as a standard sound-card. The USB audio is generic and does not require any driver install. The USB Audio also works with MAC or Linux. The USB audio is bidirectional so both playback and recording from DSPre can be simultaneous. Any input of DSPre can be recorded. Same USB is used for communication between DSPre and DSPreLab, turning DSPre into a potent speaker measurement platform. Firmware and filters are updated trough the USB connection also.

Digital inputs TOSLINK, SPDIF, AES/EBU:
Digital sources can be connected to the DSPre 1 via SPDIF (Phono 2-4 pcs.), TOSLINK (Optical 1psc.), AES/EBU (XLR 0-2 pcs.) or the above mentioned USB (1 pcs.). Digital inputs accepts Sample-rates from 11,025kHz up to 196kHz and are sample-rate converted to the internal 44,100 kHz processing rate.

Analog to Digital inputs natively, no extra cost for A/D modules:
DSPre do all the calculation digital domain and therefore analog input have to be converted into digital signals. Our preamplifier has two stereo Analog to Digital Converters for analog line signal. The ADC sensitivity can be adjusted to match the signal level of your analog source. ADC's convert to 24bit at 88,200 kHz Sample-rate.

6 analog outputs for stereo bass, mid and tweeter:
The output digital to analog converters are module based in a manner to comfort your system. For conventionally filtered speakers only one stereo DAC is used. For 2-way and 3-way systems a second and third DAC is mounted, one DAC output for every speaker unit. The DAC's are 24bit and are up-sampled to 352,800 kHz and anti-aliasing filtering is made outside the frequency band of the human ear, deemphasizing analog component performance. Volume control is achieved by lowering the DAC reference current for damping in the region 0 to -32dB, from -32dB and down the volume is adjusted inside the DAC's 24bit multiplier. This way a analog attenuator is omitted in the signal-path, and there is only a minor bit-resolution-penalty at very low listening-levels.

Band-less equalizer to tune to your preference:
The DSPreLab software includes a band-less equalizer who have more than 16000 individual frequency-discretions for setting up to 100 EQ points. This way any listeningpreference can be met. The DSPreLab software also contains a series of EQ presets to make a good startingpoint for your individual preference.

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