Tolerances 11-13 are IBA Code of Practice specifications for General Tape, Restricted
Tape and Studio Paths respectively. Although the IBA is sadly no longer in existence the
IBA Code of Practice is still considered by many to be the definitive standard for
broadcast users and it is still in widespread use.
Tolerance 14 is a Lindos specification for a domestic cassette machines. Any good
cassette machine should pass.
Cassette machines
Tolerance 15 is the specification for stereo Studer A812 tape machines running at 15ips
with IEC equalisation and 320nWb/m nominal level but it can easily be copied to a user
tolerance and modified to suit other machines, speeds or equalisations etc. (See section
5.8).
5.3 Tolerance Strings Tolerance testing Tolerance string Channel difference tolerance Limit testing Pass/fail testing
For every result value recorded by a test segment there can be a corresponding tolerance
string. Each tolerance string can specify an upper value or a range and a maximum
allowed difference between the two channels, in one of the following formats:
n Value must be less than or equal to n
±n Value must be 0±n
n m Value must lie between n and m (space or sign separate n & m)
n±m Value must be n±m
Any of these forms can be followed by a difference specifier:
<d Channels (or registers) must match within difference d
Note that the first form would normally be used for distortion, noise or crosstalk results
which must normally be below a certain limit (but there is usually no lower limit − they
cannot be too good). The second form (±n) would normally be used for frequency
response, speed error or phase results which should ideally be 0, although the third and
fourth forms are often used for frequency response results as the upper and lower limits
are often different (eg ‘+2-3’).
n, m and d may be positive or negative, although the + sign is optional. Most tolerance
limits tend to be whole numbers, although decimal places are allowed. In fact each value
may be specified to a resolution of 0.0001 in the range -9999.9999 to +9999.99 (the
decimal part can be omitted for whole numbers).
5.4 The Tolerance Definition Tolerance testing Pass/fail testing Tolerance definitions
For each segment that requires a tolerance the segment letter is specified followed by a
list of tolerance strings, one for each value measured in that segment each separated by a
comma, as in table 5.3. A list of results values for each segment, together with the
number of values produced by each segment, is shown in table 3.2 (on page 40).
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5. Tolerance Testing
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