referring to the accompanying drawings , embodiments of the present invention will be now explained . fig1 shows a major portion of an information recording apparatus as a first embodiment of the present invention for recording at least a video signal and an efm digital audio signal . the information recording apparatus of the first embodiment may record an fm audio signal in addition to the video signal and efm digital signal . in fig1 an information recording apparatus 1 is provided with : an fm modulation unit 2 , to which a video signal s v and an efm digital audio signal s da are inputted , for outputting a mixed fm modulated signal s fm ; a laser driver unit 3 for generating and outputting a recording laser pulse control signal s lp on the basis of the mixed fm modulated signal s fm ; and an optical pickup 4 for performing light - modulation on the basis of the recording laser pulse light l onto an optical disc ( i . e . laser vision disc ) ld , which is rotated by a spindle motor m . fig2 shows a construction of the fm modulation unit 2 . in fig2 the fm modulation unit 2 is provided with : a pre - emphasis circuit 10 for applying a pre - emphasis to the video signal s v and outputting it ; an fm modulation circuit 11 for fm - modulating the video signal s v , to which the pre - emphasis has been applied , and outputting it as an fm - modulated video signal s mv ; a band pass filter 12 for passing only a video band component of the fm - modulated video signal s mv and outputting it as an fm - modulated video band range signal s lmv ; a mixing circuit 13 for mixing the efm digital audio signal s da with the fm - modulated video band range signal s lmv to output a video and audio mixed signal s va ; and a limiter 14 for limiting an amplitude of the video and audio mixed signal s va to change its form into a square waveform and outputting it as a mixed fm modulated signal s sfm and also performing a symmetry adjustment by changing a limiter balance thereof . in order to improve the s / n and the ber at the time of reproduction , it is required to form a high quality , jitter - free record pit in the recording operation of the optical disc such as an ld , and to make the reproduced rf signal resemble the original signal as much as possible . to achieve this requirement , the recording duty is decreased and the recording laser power is commensurately increased . according to this method , it becomes possible to prevent to some extent the record pit from having a tear - drop shape due to heat accumulation . one embodiment uses a symmetry adjustment method to adjust the recording duties of all record pits ascending to an optimum reduction rate for the record pit which has a relatively long pit length . for example , assuming that the optimum reduction rate of the recording duty of the record pit having the relatively long pit length is x %, the recording duties of all pit lengths are reduced at the reduction rate of x %. by this symmetry adjustment , as compared with the case where the symmetry adjustment is not applied , a more ideal shape of the record pit can be realized . in fig3 the laser driver unit 3 is provided with : a δt adjustment circuit 20 for re - adjusting the recording duty corresponding to the mixed fm modulated signal s sfm outputted from the limiter 15 in accordance with the record pit which has a relatively short length ( i . e . performing a δt adjustment ); a pulse selectively inverting circuit 21 for selectively inverting and non - inverting the phase of the output signal of the δt adjustment circuit 20 ; and a laser diode driver 22 for driving a laser diode on the basis of the output signal of the pulse selectively inverting circuit 21 i . e . generating the recording laser pulse control signal s lp . by symmetry adjustment , since the recording duty is adjusted by use of a the recording duty of a pit having a relatively long pit length as the standard of the adjustment , the recording laser pulse width becomes too small with respect to a record pit having a relatively short pit length , preventing accurate pit formation . more concretely , the highest recording frequency in the ld format is as high as 9 . 3 mhz , and the optimum pit length ( which corresponds to the minimum pit length ) becomes 0 . 61 μm ( on condition that the linear velocity is 11 . 4 m / s ). thus , accurate pit formation cannot be performed if the recording duty is reduced too much in the symmetry adjustment . therefore , it is desirable to increase the pulse widths of all recording laser pulses corresponding to the recording duties after the symmetry adjustment by predetermined amount i . e . by several ns ( nanoseconds ) respectively . namely , with respect to each of the record pits , the recording duty is increased by a predetermined amount . as such , the recording duty of a relatively short record pit is apparently increased more as compared with the recording duty of a relatively long record pit , so that the optimum pit formation can be performed with respect to a relatively short record pit . fig4 shows a construction of the δt adjustment circuit 20 and a pulse selectively inverting circuit 21 in more concrete forms . in fig4 the δt adjustment circuit 20 is provided with : an ecl ( emitter coupled logic ) output comparator 31 and an ecl buffer 32 . the mixed fm modulated signal s sfm is inputted to one input terminal of the ecl output comparator 31 from the limiter 15 . another input terminal of the ecl output comparator 31 is connected to a variable standard voltage source 30 for setting cutoff voltage level to determine the δt adjustment amount i . e ., determine how much the recording laser pulse width is increased . the ecl output comparator 31 compares to the level of the mixed fm modulate signal s sfm with the level of the cutoff voltage level , and outputs a signal having the ecl level . one input terminal of the ecl buffer 32 is connected to the non - inverted output terminal of the ecl output comparator 31 . another input terminal of the ecl buffer 32 is connected to the inverted terminal of the ecl output comparator 31 . the ecl buffer 32 performs the buffering operation of those inputted signals . the selectively inverting circuit 21 has a switch sw , whose output terminal tout is connected to the laser diode driver 22 of the ecl driving type , and which selectively connects the output terminal tout with one of the output terminals of the ecl buffer 32 , according to a switching control signal sc from a controller of the information recording apparatus not shown in the figure . the laser diode driver 22 generates the recording laser pulse control signal s lp . next , the recording operation of the present embodiment will be explained with reference to fig2 to 6 . in fig2 the pre - emphasis circuit 10 applies the pre - emphasis to the video signal sv and outputs it to the fm modulation circuit 11 . by this , the fm modulation circuit 11 fm - modulates the pre - emphasized video signal sv to output the modulated video signal s mv to the band pass filter 12 . the band pass filter 12 passes only the video band component of the modulated video signal s mv and outputs it as s lmv to the mixing circuit 13 . as a result , the mixing circuit 13 mixes the modulated video band signal s lmv and the efm digital audio signal s da to produce the video audio mixed signal s va ( as shown in fig5 ), and outputs it to the limiter 14 . the limiter 14 performs amplitude control while changing the limiter balance . namely , the limiter 14 performs a symmetry adjustment of the video audio mixed signal s va by performing the amplitude control while shifting the level of the amplitude control band range . then the limiter 14 changes the form of the video audio mixed signal s va , which has been symmetry - adjusted , to a square wave , and outputs it as the mixed fm modulates signal s sfm ( as shown in fig5 ) to the δt adjustment circuit 20 of fig4 . in fig4 the ecl comparator 31 of the δt adjustment circuit 20 compares the voltage level of the inputted mixed fm modulated signal s sfm with the cutoff voltage level set by the variable standard voltage source 30 . then , if the voltage level of the inputted mixed fm modulated signal s sfm is higher than the cutoff level voltage , the output voltage of the non - inverted output terminal becomes the &# 34 ; h &# 34 ; level , and the output voltage of the inverted output terminal becomes the &# 34 ; l &# 34 ; level . this output voltage waveform of the ecl comparator 31 is changed in its waveform by the ecl buffer 32 , is inverted in its phase by the pulse selectively inverting circuit 21 as occasion demands , is applied to the laser diode driver 22 , and is outputted as the recording pulse control signal s lp from the laser diode driver 22 . by this operation , the recording laser pulse light l is irradiated from the laser diode of the optical pickup 4 , so that a record pit is formed on the optical disc ld in fig1 . fig6 shows the relationship between the standard cutoff level of the variable standard electric source and the record pit , which is actually formed on the optical disc . in fig6 the ideal form of the record pit corresponding to the waveform of the mixed fm modulated signal s sfm is a record pit p0 . on the other hand , if the cutoff voltage level of the variable standard electric source 30 is set to first level sl1 by the δt adjustment there is formed a record pit p1 with a pit length that is longer than the ideal record pit p0 by δt1 / 2 on either end . if the cutoff voltage level of the variable standard electric source 30 is set to a second cutoff voltage level sl2 by the δt adjustment , there is formed a record pit p2 with a length that is longer than the ideal record pit p0 by δt2 / 2 (& gt ; δt1 / 2 ) on either end . as such , the cutoff voltage level can be freely set at the variable standard electric source 30 by the factors such as the material of the optical disc to be recorded and the power of the recording laser light . by performing the recording operation as described above , the generation of the pit having the tear - drop shape can be prevented by reducing the recording duty if the recording frequency is relatively low ( i . e ., if the pit length is relatively long ). the record pit can be generated with a lesser reduction of the recording duty if the recording frequency is relatively high ( i . e ., if the pit length is relatively short ). as a result , it becomes possible to form record pits with low jitter , and it also becomes possible to easily detect the conversion of the pit length . in case of recording the video signal , the fm audio signal and the efm digital audio signal onto the optical disc ld of write - once - read - many type , the s / n and the ber can be improved , so that the reproduced signal waveform can closely resemble that of the original record signal . the second embodiment of the present invention is for use with an optical disc with a reflection coefficient of the record pit portion ( i . e . a portion where a record pit exists ) that is lower than the reflection coefficient of the non - recorded portion ( i . e . a portion where a record pit does not exist ). fig7 shows the characteristic of the optical disc of the second embodiment . specifically , fig7 a shows the case where the phase of the recording laser pulse control signal is inverted , while fig7 b shows the case where the phase of the recording laser pulse signal is not inverted . fig7 b , the optical disc used in the second embodiment has such a characteristic that the portion to which the laser diode is turned on i . e ., the portion where the record pit has been formed has a lower reflection coefficient than the non - recorded portion , and the record pit portion is relatively dark . as a result , the rf signal is reproduced as shown in fig7 b . the tia ( time interval analysis ) of the efm signal distribution n obtained by extracting the efm band range from this rf signal , is shown in fig8 b . each peak in fig8 b corresponds to each pit having different pit length ( i . e . 3t to 11t pit ). as shown in fig8 b , it is difficult to clearly distinguish each pit to perform the efm - reproduction ( i . e . without inverting the recording laser pulse control signal at the time of recording ), resulting in a ber that is degraded at the time of reproduction . therefore , in the second embodiment , in case of reproducing such an optical disc , the phase of the recording laser pulse control signal s lp is inverted by use of the selectively inverting circuit 21 shown in fig3 and 4 , so that the on / off of the laser diode is inverted as a result . this feature of the second embodiment is explained in more detail with reference to fig7 a . in the second embodiment , the on / off control of the laser diode is inverted as shown in fig7 a with respect to the case of fig7 b . by this , the record pit and the reproduced rf signal become as shown in fig7 a . as for this condition of fig7 a , the tia ( time interval analysis ) of the efm signal distribution n obtained by extracting the efm band range from this rf signal is shown in fig8 a . each peak in fig8 a corresponds to each pit having different pit length ( i . e . 3t to 11t pit ). as shown in fig8 a , it becomes easy to clearly distinguish each pit with respect to the case of fig8 b , to perform the more accurate efm - reproduction , resulting in an improved ber . as described above in detail , according to the present embodiments , after performing the adjustment of the recording duty by use of the recording by use of the recording duty of the pit having a relatively long pit length as a standard , the recording duty of the relatively short record pit is apparently increased as compared with the recording duty of the relatively long record pit . thus , the optimum recording duties can be obtained with respect to all of the record pits , which have various pit lengths from a short pit length to a long pit length , and the optimum pit formation can be performed with respect to all of the record pits . accordingly , the record pit can be formed without jitter , and the reproduced rf signal can resemble the original signal , so that the s / n and the ber can be improved . further , according to the present embodiments , in case of reproducing the optical disc , the efm signal can be easily extracted and distinguished , so that the accurate reproduction can be performed and the s / n and the ber can be improved at the time of reproduction . the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof . the present embodiments are therefore to be considered in all respects as illustrative and not restrictive , the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein .