CMD 42

LED feedback

The CMD 42 has an LED ring which provides visual feedback during operation. The following states are indicated:

• BOOT/REBOOT: Steady white LED for 5 seconds: During startup, the LED ring will light up in white for 5 seconds, indicating a successful startup of the microphone. The LED turns off after 5 seconds.
• COMMAND SUCCESSFUL: 3 short, green blinks: successful transmission via the Remote App. Now you can be sure that the current app settings are in the microphone!
• COMMAND FAILED: 3 short, red blinks: Incorrect transmission of commands via the remote app. This may be due, for example, to parameter values being selected in the app that older CMD 42 firmware does not understand. These values must then be avoided.
• IDENTIFY: 13 short, green blinks: Feedback to the “Identify” command of the Remote App
• WARNING: Steady yellow LED: Digital Phantom voltage too low. This can occur if you use a very long cable. If you see a steady yellow LED, try using a shorter cable and/or a proper AES cable. This error can also occur if you use a cable with in-built RF filter circuitry, which often is used when connecting analog microphones to wireless transmitters.
• NO CAPSULE: Red blinking LED: No capsule is connected. The output is muted in this case to avoid hum and buzz.

Troubleshooting

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 acoustic path is disturbed. The cell phone is too far away or too quiet.
• The cell phone is not sending intelligible commands:
  • Switch off "Spatial audio" in the audio settings of the cell phone.
  • Deactivate other sound-influencing audio settings in the cell phone such as EQ, binaural, etc.
  • If the cell phone or tablet has several loudspeakers, this can lead to a disturbing superposition. In this case, masking individual speakers can help.
• App is faulty. Reinstalling the app and checking via another mobile phone/tablet is recommended.
• Capsule is faulty: Another microphone capsule should be tried.
• CMD 42 is faulty: Microphone must be checked in service.

Settings

• Dweedle Delay: Sometimes it is desired that the playback of the acoustic signal is delayed in order to point the cell phone to the CMD 42 in good time. This can be set here. Default: 0s

Mode: “Full” vs. “Pure”

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.

• Fixed sampling rate: 48 kHz
• Supported commands: Digital Gain, Low Cut, Analog Pad, Channel Configuration (including Mono Upmix), Peak Limiter, Capsule Correction, Filter
• Latency with Peak Limiter off: 104 samples (inherent delay = 2.16 ms)
• Latency with Peak Limiter on: 152 samples (inherent delay = 3.16 ms)

“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).

• Supports all sampling frequencies up to 192 kHz (native, no upsampling!)
• Supported commands: Digital Gain, Sampling Rate, Analog Pad
• Latency: 11 samples (inherent delay = 57 μs at 192 kHz)

Identify

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.

Reset

This command resets the CMD 42 to the default factory settings. The output of the microphone is muted during this process.

Digital Gain

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.

Low Cut 24 dB/oct (Full Mode only)

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.

Analog Pad

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.

Channel Configuration (Full Mode only)

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.

• Default = Clone: Same output on both channels
• Dual: Channel 1 contains the processed signal while the raw signal is on channel 2
• Upmix:

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 strong

Upmix with a higher level of diffuse sound

Peak limiter (Full Mode only)

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:

• Threshold: -0.5 dB-FS
• Attack: 0.01 ms
• Release: 50 ms
• Look-Ahead-Delay: 1 ms

Capsule Correction (Full Mode only)

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.

Filter (Full Mode only)

• Low-frequency equalization

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").

• Proximity equalization

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.

• Omni equalization

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.

• J filter / Ribbon mode

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.

• Parabolic filters

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.

• Digital Gain and Analog Pad see above

• Sampling Rate (Pure Mode only)

The sampling rate in Full Mode is fixed at 48kHz. In Pure Mode, the sampling rate can be selected from the following options:

• 44.1 kHz
• 48 kHz
• 88.2 kHz
• 96 kHz
• 176.4 kHz
• 192 kHz

The sampling rate is generated natively within the CMD 42; no upsampling takes place.

• XT Filter (Pure Mode only)

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.