this  area are left not to headphones or loudspeakers. The centerfrequencies or the in the middle of  the notches 1 and 2 can by   the tonecontroller 1 and 2, independently, over which whole pass  band are shifted, by that "Breiten"/ Width-controllers become  the Notch or Peak areas  (cross-hatched areas) together widened or narrowed.

Doublenotch  ( Notch  2 x )
This term comes from the English language and means notch, recessing, cut etc.. With the ED88NF filters are to   t w o , independently, in the operating mode " Notch " electronically in the width adjustable and notches or holes variable in the frequency pass band for the handling of the received transmission at the disposal. Thereby it is alike whether the transmission of the receiver consists of music, language, disturbances or other signals. With the  ED88NF are let through and processed frequencies, tones or oscillations within the range between 100 Hz   and  4500 Hz. If the breakdown tone has a frequency of 1000 cycles Hz for example, it can be  notched " narrowly " or " broadly ". That is called the  tonecontroller  e.g. 1   to this spurious frequency is slowly  by hand electronically set. If the  " hole " or the " notch " is broad /width (=) (" Breiten" controller shows to the left), the  breakdown tone is faster and easier to find. If the breakdown tone  became very quiet, the notch can be placed by the "Breiten"-controller more narrowly, so that only the  spurious  frequency is filtered. One should still somewhat more exactly place behind also the appropriate  tonecontroller on the spurious frequency. So far that the too received transmission will transfer normally however without spurious signal. Switching the filter off shows the large difference  between transmissions with or without breakdown tone.

Since the ED88NF is a filter however a doublenotchfilter, it gives not only once, but twice, or depending upon width, which notchpossibility, independently, several breakdown tones. That is helpful or useful for example with teleprinter -, computer or other spurious  signals.

Double peak   ( peak 2x )
In the filter operating mode " peak " (English = point /peak) is lifted out coming in contrast to the notchoperation the desired tone or frequency range, by the receiver, like a peak and electronically or  active from the frequency composition between 100 Hz and  4500 Hz. That means it that, depending upon adjustment of the bandwidth, only one tone or only a small part speak or of the music  area is let through as steep band-pass filter. All other tones or frequencies beside the band-pass filter become with approx.  50 - 70 dB suppresses, closed or absorbed. Then e.g. only the weak or quiet  tones only one station become audible, if the bandwidth controller is on " narrowly " ( on the right =).
The center frequency of the band-pass filters 2  between 100 Hz and 4.5 kHz can be  adjusted also here   with the help of the tonecontoller 1 and It is to be noted that e.g.  with telegrafie (CW) the  band-pass  filters should be placed one above the other or with  SSTV, FAX , RTTY etc. next to each other. In the operating mode " CW " are the filters  switched into series however into the 3. Rotary switch position " peak 2x " parallel. With  telegrafie and in the filter adjustments " CW " and " peak 2x " one can with the help of the LED,  between which tonecontroller fast with max. brightness adjust the desired tone passage. The max. brightness the LED should be brought with the desired tone in consonance.
If the filtered signals are distorted, the filterinput signal is too high. The reduction of the  AF- frequency (AF/audio controller) at the receiver eliminates immediately the distortions. Thus breakdown/sensing rate is improved also again. Ring should become audible in the background in the narrowest band-pass filter or filter adjustment " rings " or, this effect can be reduced easily by small shifting of the center  frequency with the help of the tonecontoller 1 or 2. Peak and Notch (common).  This dual function is activated with the help of the small toggle switch beside the jack  headset-phone. Thus the filter 2 is  switched and adjusted as Notchfilter. This common function or or to toggle switches function only, if the rotary switch is on " CW " or " peak 2x ". With the  tonecontoller 2 hereby that is notched disturbing  on/signal and improved or raised with the  tonecontroller 1 however the desired information signal. The bandwidth controller changes the width of the notch and the peak also here together.

Another Filtering possibilities:
a)  The transmission e.g. by one hum disturbed, can both tonecontoller or also only one  controller into the area by 100 Hz be in such a way adjusted that do not hum  any longer becomes audible.
b) Here it  possible also both notches is to be next to each other placed, so that  a larger area is notched.

Rotary switch - programming:
    3 positions e.g.. a, b and c: Doublenotch, superpeak, double peak. Tap at the ring, under the supporting annular gear with the threaded end of the rotary switch in with  " 3 " marked   2nd left hole puts.

    Rotary switch position: a) Notch 2x - Telefonie, SSB, FM, AM...
    (written undertaking)   b) CW           - telegrafie, or also Telefonie
                                      c) peak   2x - RTTY, SSTV...    or also Telefonie
                                                    (narrow) with audiopeaklevel