2. Remote App (smartphone/tablet app)
3. CMD 42 settings and their properties
The CMD 42 is the digital microphone amplifier for the Schoeps Colette series. It is fully compatible with all Schoeps MK capsules. Even a >20 years old MK 4, for example, should work without any problem.
The CMD 42 is also compatible with all Colette accessories such as RC tubes, CUT filters, active cables or table stands.
It is not necessary to use a Colette PAD element, as the built-in analog pad performs the same function.
At extremely high sound pressure levels in the low frequency range, however, the use of a CUT 60 filter element is recommended to avoid overloading the analog input stage and the A/D converter. If on the other hand the analog input stage and the A/D converter do not overload, the internal Low Cut of the CMD 42 is also an option.
To reduce the risk of jitter and signal interference, make sure to use AES-specified cables with 110-Ohm characteristic impedance. Only such cables ensure optimal operation of the CMD 42. The cable length can be up to 300 meters. You can also use standard analog mike cables, but then the maximum recommended length is only 10 meters (33 feet).
To prevent excessive voltage drop in the supply voltage, multiple plug connections and long cable runs should be avoided. The CMD 42 has integrated undervoltage detection and lights up yellow if the voltage available at the microphone amplifier is too low.
The CMD 42 detects whether a capsule is connected or not (see below). The microphone mutes itself during any change so that audible distortion is reduced to a minimum. The CMD 42 cannot be damaged by connecting/disconnecting a capsule.
The CMD 42 provides visual feedback after successful booting (see below). It switches off when phantom power is switched off, and boots automatically the moment phantom power is applied. It does not matter in which order the CMD is connected to the unit and power is applied to the unit. Upon rebooting, the CMD automatically wakes up with the last previous set of settings. The boot process takes approx. 2 seconds.
The CMD consumes much more power than an analog microphone (1-2 Watts). Therefore, the microphone body can get quite warm over its entire surface. This is intentional and necessary to avoid overheating. However, you should still be able to hold the microphone in your hand. Operating temperatures of up to 40°C are normal.
The connection standard of the CMD 42 is AES42, which basically is a combination of AES3 and a 10 V digital phantom power. Compatible AES42 devices include:
Here is a list of current AES42-compatible devices.
Normally, the CMD 42 runs in Mode 1 when connected to another device. Then the microphone runs asynchronously, i.e. with its own clock. The device to which the microphone is connected must either use a sample rate converter at its input or synchronize itself to the clock of the microphone.
If an AES42 device provides Mode 2 operation, the microphone can be synchronized to that device’s clock. Operation of multiple microphones is then possible without a sample rate converter.
Connect the microphone only to microphone inputs that supply phantom power in accordance with AES42. Although the CMD 42 is protected against short-term operation on an analogue microphone input with 48V phantom power, it will not power the CMD 42 correctly, and longer connection of this kind should be avoided.
Firmware updates can currently be carried out only by Schoeps or its authorized service partners. Repairs and service work should be carried out only by authorized, specialist personnel. Unauthorized opening or modifications of the microphone will invalidate the warranty.
Repairs and service work should only be carried out by authorized, specialized personnel. Unauthorized opening or modification of the microphone will void the warranty.
Firmware updates can currently only be carried out by Schoeps or authorized service partners. Firmware updates and the associated shipping costs are subject to a charge. The version of the firmware is given in the manual that accompanies the amplifier on delivery.
Firmware History:
The Remote App can be used to control the CMD 42. The app uses the speaker of your smartphone to send an acoustic signal that is understood by the CMD 42 microphone amplifier.
App Quick start:
In practice, the communication range is limited to < 1-2 meters, because the room reverb makes the signal too blurry. Each CMD 42 must be addressed by its serial number in order to receive a control signal.
The CMD 42 has an LED ring which provides visual feedback during operation. The following states are indicated:
If there is no LED feedback after an acoustic transmission of commands via the Remote App, the transmission has failed. This can have the following causes:
The CMD 42 has two overall modes of operation. You can switch between these two modes only via the Remote App.
“Full” Mode offers all signal processing capabilities but is locked to a 48 kHz sample rate.
“Pure” Mode is designed for low-latency operation, and ensures that there is no signal processing active in the microphone (one exception: the XT filters above 20 kHz).
This command can be used to identify a CMD 42. When it is selected and sent to the CMD 42, its LED flashes green for a few seconds. It can also be used to verify stable communication with the app, since it doesn’t interrupt or change the audio in any way, but simply provides a reassuring visual response.
This command resets the CMD 42 to the default factory settings. The output of the microphone is muted during this process.
This setting applies digital gain to the audio signal before the limiter. You can use the gain to drive some signal level into the limiter and to get a more production-appropriate volume.
Note that, unlike the analog gain of a microphone preamp, higher digital gain never improves dynamics. Digital gain is NOT used to avoid noise. Digital amplification is used only to bring the signal into a usable working range, e.g. if downstream devices have too little gain (such as a headphone amplifier) or have a lower dynamic range (such as a radio link).
The optimum dynamic range of the CMD 42 is achieved with a digital gain of 0 dB. This is because the higher the digital gain, the lower the maximum sound pressure level above which the signal is overdriven or driven into the limiter.
This 4th-order digital low-cut filter has a slope of 24 dB/octave. The -3 dB cutoff frequency can be set between 20 Hz and 160 Hz. The filter can be switched "Off"; then only a permanent analog high-pass filtering at approx. 8 Hz is active. The default value is 20 Hz to avoid infrasound interference.
The low-cut is placed in the signal chain before digital amplification, so that low-frequency noise is successfully filtered out before the signal is amplified.
The analog pad reduces the polarization voltage of the capsule in three steps. This allows you to achieve even higher maximum sound pressure levels without overdriving the input stage of the CMD 42. Settings of "0 dB" (Off), "-6 dB", "-12 dB" and "-18 dB" are possible.
The analog pad leads to an increase of the maximum possible sound pressure level, but at the same time, to an increase of the inherent noise by about the same value.
The CMD 42 provides a two-channel digital output signal, although there is only one capsule and one audio signal. Therefore, the sound engineer can choose the content of the redundant second channel.
The SCHOEPS Upmix Plugin is very well suited to better integrate mono signals into a stereophonic mix. It decorrelates the diffuse part of the audio signal, making it more natural. A similar upmix algorithm is included in the CMD 42. When the upmix is active, the microphone outputs a stereo signal (without coloration: either leg of the stereo signal can be further used as a good mono signal).
Upmix with a higher level of diffuse sound
The peak limiter limits the output signal to -0.5 dB-FS and prevents digital clipping after the digital gain. The output signal of the limiter goes to the upmix algorithm (if activated). Regardless of how high the digital gain is in the CMD, the output signal is never overdriven when the limiter is activated.
The limiter adds another 1 ms of latency to the signal.
Please note that the limiter cannot protect the analog input of the CMD 42 from overloads caused by extremely high sound pressure levels; in such cases the integrated "Analog Pad" must be used.
Settings of the Peak Limiter:
Future capsules will optionally contain a capsule memory module in which the properties of the capsule are stored, and which the CMD 42 can read out. At this moment, the capsule memory is not yet available.
Among other information, the frequency response and sensitivity of the capsule is stored. This information can optionally be used to normalize the response of the capsule.
"Off" means: the frequency response of the capsule is not normalized; the capsule signal is recorded “as is”.
"On" means: the CMD 42 normalizes the sensitivity and frequency response of the capsule if it contains a memory module. In this way, all capsules and capsule types will have the same sensitivity, and all capsules of a given type will have the same frequency response. This has the same effect as if all the capsules were perfectly matched.
A pressure gradient capsule (=directional capsule) such as a cardioid capsule has an inherent low frequency loss. This is often perceived as natural, and to some extent it is also automatically compensated for by proximity effect.
However, there are applications where a flat free-field frequency response (in the far field) is desired. This can be corrected with an appropriate correction filter which boosts the low frequencies depending on the capsule type.
Correction filters are available for: wide cardioid ("21 flat"), open cardioid ("22 flat"), cardioid ("4 flat"), supercardioid ("41 flat") and figure-8 ("8 flat").
Due to proximity effect, low frequencies are boosted when the sound source is very close to the microphone. This boost is compensated by these low-frequency attenuation filters. There are - equivalent to our "P" capsule types - two different levels of correction: "P" (moderate correction) and "XP" (strong correction). The filters have a sloping frequency response below 200 Hz.
Schoeps offers several capsules with omnidirectional characteristics, which differ in the degree of diffuse-field equalization. The MK 2 has a flat on-axis frequency response, while the MK 2H (+2dB @ 10 kHz), MK 2S (+3dB @ 10 kHz) and MK 2XS (+5dB @ 10 kHz) types compensate for the loss of high frequencies in the diffuse field. These omnidirectional capsule types actually differ only by an acoustic filter, the polar diagram is the same in each case.
The omni equalization filters in the CMD 42 make it possible - when using an MK 2 - to produce the frequency responses of the MK 2H, 2S and 2XS.
The "J" filter is a Schoeps special that emulates the character of a ribbon microphone. The equalization was originally developed for recording the Japanese shamisen with its great concentration of high frequency sound energy. The filter attenuates frequencies above 10 kHz.
These filters compensate for the high-frequency boost which occurs when the Schoeps parabolic dish set is used with the MK 2 or MK 4 capsule. The following setup with a CMD 42, an active cable KC and an MK capsule was made with a "Telinga Modular" dish and a mechanical adapter.
The sampling rate in Full Mode is fixed at 48kHz. In Pure Mode, the sampling rate can be selected from the following options:
The sampling rate is generated natively within the CMD 42; no upsampling takes place.
The XT filter is a high-frequency boost which linearizes the frequency response of the microphone capsules at frequencies between 20 kHz and 50 kHz. The filter requires a sampling rate >= 96 kHz. It is useful in combination with the "forward-facing" capsules MK 2 (H/S/XS), 21, 22, 4 and 41.
The filter corresponds to the one in the analog CMC 6xt amplifier.
Its use is recommended at high sampling rates, especially when the signal is to be transformed into the audible range by downpitching (as is common in sound design). The CMD 42 has an exceptionally high dynamic range and low noise floor even above 20 kHz, which makes it very suitable for these tasks.
As the XT filter drops out above 50 kHz, it should not be used if signal content is desired there. MK capsules do have a significant signal level up to over 100 kHz! It is then advisable to use a shelving filter in post-production instead of the XT filter above 15 kHz.
