Byte-by-byte allocated data manipulation

[Mirage]

I recommend to use dynamic arrays.

SetLength(Samples[j].SampleData, Samples[j].SampleLength); // Instead of GetMem
if Samples[j].SampleLength > 0 then BlockRead(FileStream, Samples[j].SampleData[0], Samples[j].SampleLength * SizeOf(Samples[j].SampleData[0]));

where Samples[j].SampleData is declared like this:

SampleData: array of Byte; // or whatever you want instead of byte

Of course you can manipulate with the array data as you wish.