Conference napalm::commusic_v1

This is a very interesting topic, Karl the tooth.  I've never banged around
with a sampler (well, not much anyways) and have never thought about some 
of the things you mentioned in .0 until I read them.

It seems that you have just exposed yet another sampler/computer software
market niche.  When is someone gonna come out with a waveform editor for
a sampler that automatically induces some sort of stereo effect by cloneing
the waveform and modifying the clone to create a similar but different waveform 
(either in shape, or in time alignment, or ???)?  Channel A would be 
assigned the original waveform, and channel B would get the clone...  
Of course, all the 'hot rod' samplers/waveform_editors probably already do 
this.

Another idea is to sample a sound direct, and assign that sample to channel
A.  Sample the same sound via amp and mics (induced room ambience) and assign
that to channel B...  

I think that minute time shifting between channels is probably the easiest and 
most effective method of creating a stereo image, and is the technique I
use most in recording.  The EQ idea is interesting - I'll have to try that
next...

Todd.

>Another idea is to sample a sound direct, and assign that sample to channel
>A.  Sample the same sound via amp and mics (induced room ambience) and assign
>that to channel B...  

right ! this can also be done as a regular tape production trick either
    as you described, while recording, or during mixdown, where the
    left channel is direct/clean, and the right channel is either run
    into a room with a speaker and monitored, or by run into a delay 
    with some different EQ.
    
    I was playing some patches on an Emax the other day and there was
    a 'stereo Strat' sound.. a bit thin, but as you said, they'd taken
    it straight in the left channel and timedelayed it in the right.
    I agree, time delay, rather than EQ, is our primary way to perceive 
    signals as 'being in stereo'.. so save those tape tracks and use
    those digital delays in new and wondrous ways !

    First of all, let me say, that my belief is that there is nothing
    better than stereo miking and recording for achieving and preserving 
    an image that is closest to what our ears hear; of course this 
    applies to voice and acoustic instruments more than electronic.
    
    However, a good way to create a stereo field, is to run the signal
    through a very short delay like ~.0005 sec. then mix the original
    with the delayed signal to get the right channel, and reverse the
    phase of the delayed signal and mix it with the original to get
    the left channel.
    
    Cancellations and reinforcements of the waveform occur giving you
    something similar to, but much higher resolution than, the boosting
    and reducing of alternate frequencies on an eq.
    
    Also, a great advantage of this method, is that when the music gets
    played mono, the delayed signal just cancels out leaving you with
    the original. 
    
    Fredric    DVINCI::CERTO
      

>    However, a good way to create a stereo field, is to run the signal
>    through a very short delay like ~.0005 sec. then mix the original
>    with the delayed signal to get the right channel, and reverse the
>    phase of the delayed signal and mix it with the original to get
>    the left channel.
>    Also, a great advantage of this method, is that when the music gets
>    played mono, the delayed signal just cancels out leaving you with
>    the original. 

    Forgive my ignorance, but I thought that mixing out-of-phase signal
    especially in mono - led to cancellation of bass frequencies and
    general weirdness... and, what hardware would typically allow such
    an effect ? SPX90 ? 
    
    Regarding 'stereoizing' a mono signal using a stereo 10 band graphic
    EQ like this ::
>........left channel..............    ..........right channel...........
>  ^    |    ^    |   ^     |   ^        |   ^    |    ^    |    ^    |
>  |    v    |    v   |     v   |        v   |    v    |    v    |    v
>oct1 oct2 oct3 oct4 oct5 oct6 oct7    oct1 oct2 oct3 oct4 oct5 oct6 oct7
    I checked the stereo output on a small oscilloscope I have and the
    resulting stereo spread was more impressive than running the signal
    thru a stereo phase shifter. Granted, the signal doesn't 'move'
    the way a chorus would, but the difference between the sides is
    noticeable, not striking.       
    
    karl

    The reason you are cautioned to be sure you hook up your stereo
    system in proper phase is exactly as you mention - possible loss
    of bass.  That's because bass is much less directional than the
    mid and high frequencies, and this is in turn because of the longer
    wavelengths.  I.e., it's more likely that the bass information in
    the two channels is more closely in phase, and hence more likely
    to cancel if allowed to merge in an out of phase fashion (either
    in the air on the way to your ears, or in the wire if you "wire
    or" the two channels together).  Except for these kinds of gross
    cancellation effects, the ear seems to be rather indifferent to
    phase otherwise.  Also, cancellation due to phase differences in
    "through the air" transmission are much less an all or nothing thing
    than than cancellation when you wire the two channels together,
    as they will depend very stringly on the listener's position as
    long as the two sound sources are not in exactly the same place.
    
    In Fred's scheme, only the delayed signals are out of phase relative
    to one another - the direct or "dry" signals are in phase; hence
    when the two channels are added, the delayed signals cancel each
    other but the direct signals just add.
    
    Also, as I believe somebody already noted, adding delay (especially
    a short delay) produces much the same effect as the EQ scheme Karl
    proposed, due to the "comb filtering" effect of adding a delayed
    copy of a signal, although the effect on frequency response is much
    more complicated (the notches are very deep and get closer together
    as the frequency increases; hence the name "comb filtering", because
    a frequency response plot bears a vague resemblance to a comb). It is
    the movement of these notches' center frequencies as the delay changes
    that produces the effects known as phasing and flanging.

    That was a good explanation of a comb filter by Len.  When you
    alternately boost/cut your eq, you are kind of simulating two
    comb filters: one has tooth (a boost) where the other one has
    a lack of one (a cut).
    
    By delaying the signal as I suggest, the phase is altered with 
    respect to the original.  Note that the degree of phase change
    is different depending upon the frequency; so when the delayed
    signal is added with the original, some frequencies will be in 
    phase causing reinforcements, and some frequencies will be out 
    of phase causing cancellations, etc.
    
    If you have an SPX-90, you already have a variety of Stereo 
    producing capabilities, which are probably based upon this same
    idea (and a few others).  Otherwise, if you have a digital delay, 
    or slapback echo, you still need a way to reverse the phase.  Some 
    mixers can do it, or you can build a simple inverting op-amp
    circuit, or if you are running lo-Z cables, just switch the two 
    hot leads.  Or there's this thing you can do with your eq... :-)
    
    Fredric      DVINCI::CERTO            
    

    Well, it looks like we scooped KEYBOARD magazine again. In the latest
    issue, April '87, there is an article titled 'Stereo Sampling',
    which, you guessed it, details methods for deriving true stereo
    samples from a 'mono' sampler with left-right outputs. 
    
    In the same issue:
    Also, regarding the stereo 'comb filter', in Bobby Nathan's column,
    'In the Studio', he details methods for 'stereoizing' mono signals
    and indeed even has a picture of the mixer setup to do same.
    
    COMMUSIC Notes : AT THE LEADING EDGE !

    KMII : AT THE LEADING EDGE

>                                -< Correction >-
>
>    KMII : AT THE LEADING EDGE

    True, true. It's just that modesty forbade me...
    
    karl